Noise filter and electronic device using noise filter

ABSTRACT

Comprising a magnetic member  32  formed by laminating magnetic sheets  24, 28, 30, 31  a first impedance element  21  formed in the magnetic member  32,  and a second impedance element  25  formed above the first impedance element  21,  the first impedance element  21  includes a first normal impedance element  22  and a first common impedance element  23,  and the second impedance element  25  includes a second common impedance element  26  and a second normal impedance element  27.

TECHNICAL FIELD

The present invention relates to a noise filter used as noisecountermeasure in cellular phone or other information devices, and anelectronic device using this noise filter.

BACKGROUND ART

A conventional noise filter is disclosed, for example, in JapaneseLaid-open Patent No. 8-335517.

FIG. 35 is a perspective exploded view of the conventional noise filter(laminated common mode choke coil). A first coil 1 and a second coil 2formed above the first coil 1 are spirally formed, and made of silver.

An insulating sheet 3 is formed beneath the first coil 1, and isprovided with two via holes 4, 5. A second insulating sheet 6 is formedbetween the first coil 1 and second coil 2, and is provided with one viahole 7. The first insulating sheet 3 and second insulating sheet 6 aremade of insulating material such as polyimide.

A first external electrode 8 disposed at one end of the first coil 1,and a first via electrode 8 a at other end of the first coil 1 areformed on the same plane as the first coil 1. A second externalelectrode 9 is formed beneath the first insulating sheet 3. A second viaelectrode 9 a is formed beneath the first insulating sheet 3, and thesecond external electrode 9 is connected to the first via electrode 8 athrough the via hole 4 provided in the first insulating sheet 3, secondvia electrode 9 a, and a first leading-out portion 10 formed beneath thefirst insulating sheet 3.

A third external electrode 11 provided at one end of the second coil 2,and a third via electrode ha provided at other end of the second coil 2are formed on a same plane as the second coil 2.

A fourth external electrode 12 is provided beneath the first insulatingsheet 3. A fourth via electrode 12 a is formed beneath the firstinsulating sheet 3, and the fourth external electrode 12 is connected tothe second coil 2 through the via hole 7 formed in the second insulatingsheet 6, via hole 5 formed in the first insulating sheet 3, fourth viaelectrode 12 a, and a second leading-out portion 13 formed beneath thefirst insulating sheet 3. That is, the second external electrode 9 andfourth external electrode 12 are formed on a same plane. The firstexternal electrode 8, second external electrode 9, third externalelectrode 11, and fourth external electrode 12 are partly exposed to theend surface of the first insulating sheet 3 and second insulating sheet6.

A specified number of third insulating sheets 14 are formed beneath thesecond external electrode 9 and fourth external electrode 12 and abovethe first coil 1, and are made of ferrite.

In this conventional noise filter, when a common mode noise is appliedto the first coil 1 and second coil 2, the impedance values of the coils1, 2 are raised, and the common mode noise is removed.

In the conventional noise filter, however, the common mode impedancecannot be raised higher.

That is, end portions of the first coil 1 and second coil 2 (the secondexternal electrode 9 connected to the first coil 1 and fourth externalelectrode 12 connected to the second coil 2) are drawn out in the samedirection (downward). It hence leads to possibility of short-circuitingof the via holes 5 and 7 for connecting the first via electrode 8 aformed in the first coil 1, second coil 2, fourth via electrode 12 a,and fourth external electrode 12. If short-circuited, the first coil 1and second coil 2 are electrically connected, and the common mode noiseremoving characteristic may not be obtained. It is therefore necessaryto keep a certain spacing 15 between the first via electrode 8 a and viahole 7, and a conductor extending from the first coil 1 cannot beprovided in this spacing 15 and the first coil 1 and second coil 2cannot be overlaid in the area corresponding to the spacing 15, and theoverlapping region of the first coil 1 and second coil 2 cannot beincreased further.

Moreover, if the current flow directions are reverse in the first coil 1and second coil 2, the magnetic fluxes generated in the first and secondcoils cancel each other, and the impedance of normal mode cannot beraised.

A different conventional common mode noise filter is disclosed, forexample, in Japanese Utility Model Publication No. 7-45932.

FIG. 36 is a perspective exploded view of the conventional common modenoise filter (laminated coil).

In a main body 201, a first coil and a second coil are formed. Upper andlower electrodes 202 and 203 are disposed on both sides of the main body201. Magnetic shield layers 204, 205 are provided in the outermost layerof the common mode noise filter. That is, the conventional common modenoise filter is composed of the main body 201, electrodes 202, 203, andmagnetic shield layers 204, 205.

The main body 201 is composed of plural magnetic sheets for first coil206, 207, 208, and magnetic sheets for second coil 209, 210, 211. Themagnetic sheets for first coil 206 to 208 and magnetic sheets for secondcoil 209 to 211 are alternately disposed.

Specifically, the magnetic sheet for second coil 211, magnetic sheet forfirst coil 208, magnetic sheet for second coil 210, magnetic sheet forfirst coil 207, magnetic sheet for second coil 209, and magnetic sheetfor first coil 206 are laminated sequentially from the bottom.

On the top of the magnetic sheets 206 to 211, conductor patterns forforming the first coil 212, 213, 214, and conductor patterns for formingthe second coil 215, 216, 217 are printed in a square shape of nearlyone turn.

A terminal end 212 b of the conductor pattern 212 formed in the magneticsheet 206 is electrically connected to an initial end 213 a of theconductor pattern 213 formed in the magnetic sheet 207 by way of athrough-hole 212 c of the terminal end 212 b and a through-hole 209 a ofthe magnetic sheet 209.

Also, a terminal end 213 b of the conductor pattern 213 formed in themagnetic sheet 207 is electrically connected to an initial end 214 a ofthe conductor pattern 214 formed in the magnetic sheet 208 by way of athrough-hole 213 c of the terminal end 213 b and a through-hole 210 a ofthe magnetic sheet 210.

Similarly, a terminal end 215 b of the conductor pattern 215 formed inthe magnetic sheet 209 is electrically connected to an initial end 216 aof the conductor pattern 216 formed in the magnetic sheet 210 by way ofa through-hole 215 c of the terminal end 215 b and a through-hole 207 aof the magnetic sheet 207.

Further, a terminal end 216 b of the conductor pattern 216 formed in themagnetic sheet 210 is electrically connected to an initial end 217 a ofthe conductor pattern 217 formed in the magnetic sheet 211 by way of athrough-hole 216 c of the terminal end 216 b and a through-hole 214 a ofthe magnetic sheet 208.

In this way, the first coil composed of conductor patterns 212 to 214 ofmagnetic sheets 206 to 208, and the second coil composed of conductorpatterns 215 to 217 of magnetic sheets 209 to 211, in the same phase andsame number of turns as the first coil, are formed in every other layer.

The upper electrode 202 is composed of magnetic sheets 218, 219, and220. On the magnetic sheets 218 to 220, leading-out electrode conductorpatterns 221 a, 221 b, 221 c, 222 a, 222 b, 222 c are formedrespectively.

The leading-out electrode conductor patterns 221 a to 221 c are mutuallyconnected by way of through-hole, and are further connected with theinitial end 212 a of the conductor pattern 212 of the magnetic pattern206 for forming the first coil.

Similarly, the leading-out electrode conductor patterns 222 a to 222 care mutually connected by way of through-hole, and are further connectedwith the initial end 215 a of the conductor pattern 215 of the magneticpattern 209 for forming the second coil.

In this manner, on the upper electrode 202, a first coil leading-outelectrode terminal T1 a, and a second coil leading-out electrodeterminal T2 a are formed.

Further, the lower electrode 203 is composed of magnetic sheets 223,224, and 225. On the magnetic sheets 223 to 225, leading-out electrodeconductor patterns 226 a, 226 b, 226 c, 227 a, 227 b, 227 c are formedrespectively. (227 b, 227 c are not shown.)

The leading-out electrode conductor patterns 226 a to 226 c are mutuallyconnected by way of through-hole, and are further connected with theterminal end 214 b of the conductor pattern 214 of the magnetic pattern208 for forming the first coil.

Similarly, the leading-out electrode conductor patterns 227 a to 227 care mutually connected by way of through-hole, and are further connectedwith the terminal end 217 b of the conductor pattern 217 of the magneticpattern 211 for forming the second coil.

In this manner, on the lower electrode 203, a first coil leading-outelectrode terminal T1 b, and a second coil leading-out electrodeterminal T2 b are formed.

In this conventional common mode noise filter, when a common mode noiseis applied in the first coil and second coil, the impedance values ofthe coils are raised, and the common mode noise is removed.

In the conventional common mode noise filter, however, the common modeimpedance cannot be raised further.

That is, of the square-shaped conductor patterns 212 to 217, for examplerelating to the pattern 212 for composing the first coil, since theinitial end 212 a is formed inside of the terminal end 212 b, theconductor pattern between the initial end 212 a and the folded portion212 d of the conductor pattern 212 cannot be overlaid on the conductorpattern 215 for forming the second coil in the top view, and thereforethe magnetic flux generated by the first coil and the magnetic fluxgenerated by the second coil cannot reinforce each other efficiently.

SUMMARY OF THE INVENTION

The invention is intended to solve the problems of the prior art, and itis hence an object thereof to present a noise filter of high removingcharacteristic of both common mode noise and normal mode noise, capableof enhancing the impedance in both common mode and normal mode, and anelectronic device using such noise filter.

It is also an object thereof to present a noise filter of high removingcharacteristic of common mode noise, capable of enhancing the impedancein the common mode further, and an electronic device using such commonmode noise filter.

To achieve the objects, the noise filter in a first aspect of theinvention (embodiments 1, 2 described below) comprises a magnetic memberformed by laminating magnetic sheets in vertical direction, a firstimpedance element formed inside the magnetic member, a second impedanceelement formed above the first impedance element, and externalelectrodes formed at both ends of the magnetic member and connectedelectrically to each end of the first and second impedance elements, inwhich the first impedance element includes a first normal impedanceelement and a first common impedance element connected electrically tothe first normal impedance element above the first normal impedanceelement, the second impedance element includes a second common impedanceelement and a second normal impedance element connected electrically tothe second common impedance element above the second common impedanceelement, and the first common impedance element and second commonimpedance element are opposite to each other, and are insulated. In thisconfiguration, the impedance value can be heightened in both common modeand normal mode.

To achieve the objects, the noise filter in a second aspect of theinvention (embodiments 3, 4, 5 described below) comprises a magneticmember formed by laminating magnetic sheets in vertical direction, afirst coil formed by laminating plural first inner conductors, a secondcoil formed by laminating plural second inner conductors, and externalelectrodes formed at both ends of the magnetic member and connectedelectrically to each end of the first and second coils, in which themagnetic member incorporates a first laminated body composed of thefirst inner conductors, a second laminated body formed on the top of thefirst laminated body, having the first inner conductors and second innerconductors laminated alternately, and a third laminated body formed onthe top of the second laminated body, composed of the second innerconductors. In this configuration, the impedance value can be heightenedin both common mode and normal mode.

To achieve the objects, the common mode noise filter in a third aspectof the invention (embodiment 6 described below) comprises a magneticmember formed by laminating magnetic sheets in vertical direction, afirst coil formed by laminating plural first inner conductors, a secondcoil formed by laminating plural second inner conductors formedalternately with the first inner conductors, and overlapping with thefirst coil in a top view of the magnetic member, and plural via holesformed in the magnetic sheets for connecting the first inner conductorsmutually or the second inner conductors mutually, in which the via holesfor connecting the first inner conductors mutually overlap with thesecond coil in a top view of the magnetic member, the via holes forconnecting the second inner conductors mutually overlap with the firstcoil in a top view of the magnetic member, and the first innerconductors and at least one of the second inner conductors adjacent tothe first inner conductors are formed to overlap almost with each otherin a top view of the magnetic member. In this configuration, theimpedance value can be heightened more in common mode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective exploded view of a noise filter in embodiment 1of the invention;

FIG. 2( a) is a sectional view along line A—A of the noise filter;

FIG. 2( b) is a perspective view of the noise filter;

FIG. 3( a) is a diagram showing impedance characteristics when currentof normal mode and common mode is applied to the noise filter;

FIG. 3( b) is a diagram showing a measuring circuit of impedancecharacteristics when current of normal mode and common mode is appliedto the noise filter;

FIGS. 4( a) to (d) are top views of conductors in the noise filter;

FIG. 4( e) is a sectional view of other example of the noise filter;

FIG. 5( a) is an equivalent circuit diagram of the noise filter (patternA);

FIG. 5( b) is an equivalent circuit diagram of the noise filter (patternB);

FIG. 6( a) is a diagram showing impedance characteristics (attenuationcharacteristics) when normal mode current is applied to the noise filterof pattern A and noise filter of pattern B;

FIG. 6( b) is a diagram showing the direction of the current applied ineach pattern, simulating noise filters of pattern A and pattern B;

FIGS. 7( a) to (f) are perspective views showing a manufacturing methodof the noise filter;

FIG. 8 is a diagram showing the relation of distance between secondconductor and third conductor, coupling coefficient, and withstandvoltage of the noise filter;

FIG. 9 is a sectional view of other example of the noise filter;

FIG. 10 is a diagram of frequency characteristics showing elevation ofimpedance value in high frequency region;

FIGS. 11( a), (b) are sectional views of other example of the noisefilter;

FIGS. 12( a) to (d) are top views of other example of the noise filter;

FIG. 13 is a sectional view of other example of the noise filter;

FIGS. 14( a), (b), (d), (e) are top views of conductors of a noisefilter in embodiment 2 of the invention;

FIGS. 14( c), (f) are pattern see-through diagrams of the noise filter;

FIG. 15( a) is a diagram showing a waveform of carrier in a pair ofsignal lines in a cellular phone;

FIG. 15( b) is a diagram showing the manner of use of the noise filterin embodiments 1 and 2 of the invention;

FIG. 15( c) is a diagram showing attenuation characteristics when thenoise filter in embodiments 1 and 2 is used in a pair of signal lines ina cellular phone;

FIG. 16 is a perspective exploded view of a noise filter in embodiment 3of the invention;

FIG. 17( a) is a sectional view of line A—A of the noise filter;

FIG. 17( b) is a perspective view of the noise filter;

FIG. 18 is an equivalent circuit diagram of the noise filter inembodiments 3 and 4 of the invention;

FIG. 19( a) is a diagram showing the relation of the number of turns andcoupling coefficient of internal conductors in a second laminated bodyas the essential part thereof;

FIG. 19( b) is a diagram showing the relation of the number of turns andcoupling coefficient of internal conductors in a first laminated bodyand a third laminated body as the essential parts thereof;

FIGS. 20( a) to (g) are perspective views showing a manufacturing methodof the noise filter;

FIG. 21 is a perspective exploded view of the noise filter in embodiment4 of the invention;

FIG. 22 is a perspective exploded view of a noise filter in embodiment 5of the invention;

FIG. 23( a) is a sectional view of line A—A in FIG. 22;

FIG. 23( b) is a top see-through diagram of the noise filter;

FIG. 24 is a sectional view of other example of the noise filter;

FIGS. 25( a), (b) are top see-through diagrams of other example of thenoise filter;

FIG. 26( a) is a perspective exploded view of other example of the noisefilter;

FIG. 26( b) is a sectional view of line A—A in other example of thenoise filter;

FIG. 27 is an equivalent circuit diagram of the noise filter;

FIG. 28( a) is a sectional view of the noise filter (pattern A) inembodiments 3 to 5;

FIGS. 28( b), (c) are sectional views of the noise filter of pattern B;

FIG. 28( d) is a diagram showing the relation of frequency andattenuation of noise filters of pattern A and pattern B in embodiments 3to 5;

FIG. 29 is an equivalent circuit diagram of the noise filter of patternB in a comparative example;

FIG. 30 is a perspective exploded view of common mode noise filter inembodiment 6 of the invention;

FIG. 31( a) is a sectional view of line A—A;

FIG. 31( b) is a perspective view thereof;

FIGS. 32( a) to (c) are perspective views showing the manufacturingmethod;

FIGS. 33( a) to (d) are perspective views showing the manufacturingmethod;

FIG. 34( a) is a diagram showing a waveform of carrier in a pair ofsignal lines in a cellular phone;

FIG. 34( b) is a diagram showing an example of the manner of use of thecommon mode noise filter in embodiment 6 of the invention;

FIG. 34( c) is a diagram showing the relation of frequency andattenuation amount when the common mode noise filter in embodiment 6 isused in a pair of signal lines in a cellular phone;

FIG. 35 is a perspective exploded view of a conventional noise filter;and

FIG. 36 is a perspective exploded view of a conventional common modenoise filter.

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1)

A noise filter in embodiment 1 of the invention is explained byreferring to the accompanying drawings.

FIG. 1 is a perspective exploded view of a noise filter in embodiment 1of the invention, FIG. 2( a) is a sectional view along line A—A of thenoise filter, and FIG. 2( b) is a perspective view of the noise filter.

Hereinafter, the first impedance element is supposed to be a first coil,the second impedance element to be a second coil, the first normalimpedance element to be a first conductor, the first common impedanceelement to be a second conductor, the second common impedance element tobe a third conductor, and the second normal impedance element to be afourth conductor.

In FIG. 1 and FIG. 2, a first coil 21 is composed of a spiral firstconductor 22 and a spiral second conductor 23 formed above the firstconductor 22. The first conductor 22 includes a first leading-outportion 22 a and a first via electrode 22 b positioned in the center ofthe vortex, and the second conductor 23 includes a second leading-outportion 23 a and a second via electrode 23 b positioned in the center ofthe vortex. The first conductor 22 and second conductor 23 are formed sothat, when a current flows in between the leading-out portions 22 a, 23a, the current flowing in the first conductor 22 and second conductor 23may be in the same direction (clockwise or counterclockwise) in a planview as seen from above the second conductor 23. The leading-outportions 22 a, 23 a are formed at opposite positions to the mutuallyplane direction.

The square first magnetic sheet 24 is formed between the first conductor22 and second conductor 23, and has a first via hole 24 a. A first viaelectrode 22 b and a second via electrode 23 b are mutually connectedthrough the first via hole 24 a, and the first conductor 22 and secondconductor 23 are connected, thereby forming the first coil 21.

A second coil 25 is composed of a spiral third conductor 26 and a spiralfourth conductor 27 formed above the third conductor 26. The thirdconductor 26 includes a third leading-out portion 26 a and a third viaelectrode 26 b positioned in the center of the vortex, and the fourthconductor 27 includes a fourth leading-out portion 27 a and a fourth viaelectrode 27 b positioned in the center of the vortex. The thirdconductor 26 and fourth conductor 27 are formed so that, when a currentflows in between the leading-out portions 26 a, 27 a, the currentflowing in the third conductor 26 and fourth conductor 27 may be in thesame direction (clockwise or counterclockwise) in a plan view as seenfrom above the fourth conductor 27. The leading-out portions 26 a, 27 aare formed at opposite positions to the mutually plane direction, and inthe same direction as the leading-out portions 26 a, 22 a.

The square second magnetic sheet 28 is formed between the thirdconductor 26 and fourth conductor 27, and has a second via hole 29. Athird via electrode 26 b and a fourth via electrode 27 b are mutuallyconnected through the second via hole 29, and the third conductor 26 andfourth conductor 27 are connected, thereby forming the second coil 25.

In FIG. 2( a), the first via hole 24 a and second via hole 29 are nearlythe same position in a top view, but they may be located at mutuallydeviated positions in a top view.

The conductors 22, 23, 26, 27 are made of conductive material such assilver or copper, and their length, width and thickness may be adjustedto conform to the specified characteristics. By using copper, the bakingprocess mentioned below can be omitted, or by using silver, baking canbe done in air atmosphere. The spiral conductors 22, 23, 26, 27 areformed on a same plane. The overall dimensions (vertical and lateraldimensions excluding the leading-out portions 22 a, 23 a, 26 a, 27 a),conductor pitch, and number of turns are nearly equal. That is,excluding the leading-out portions 22 a, 23 a, 26 a, 27 a, theconductors 22, 23, 26, 27 are nearly identical in shape. However, theoutward direction from the center of the first spiral conductor 22 andthird spiral conductor 26 is counterclockwise in a plan view as seenfrom above the fourth conductor 27, whereas the second conductor 23 andfourth conductor 27 are clockwise.

Further, the second conductor 23 and third conductor 26 are opposite toeach other, and are mutually insulated. When a current flows from theleading-out portions 22 a, 26 a drawn in the same direction into theleading-out portions 23 a, 27 a, they are formed so that the current mayflow in the same direction (clockwise or counterclockwise) in the secondconductor 23 and third conductor 26 in a plan view as seen from abovethe fourth conductor 27 (above the magnetic member 32 mentioned below).

By forming the conductors 22, 23, 26, 27 in such configuration, one end(second via electrode 23 b or third via electrode 26 b) of the secondconductor 23 or third conductor 26 is connected individually in thevertical direction (the second conductor 23 to the first conductor 22beneath, the third conductor 26 to the fourth conductor 27 above), sothat there is no possibility of short-circuiting of the second conductor23 and third conductor 26. Accordingly, unlike the conventional noisefilter, the second conductor 23 and third conductor 26 can be extendedby a necessary portion, and further the second conductor 23 and thirdconductor 26 are formed spirally, so that the overlapping region of thesecond conductor 23 and third conductor 26 can be increased. As aresult, when the current flows in the same direction in the secondconductor 23 and third conductor 26, the magnetic fluxes generated inthe second conductor 23 and third conductor 26 can be mutuallyreinforced, so that the impedance value in the common mode can beheightened.

Further, if the current flows in reverse directions in the secondconductor 23 and third conductor 26 and the magnetic fluxes generated inthe second conductor 23 and third conductor 26 cancel with each other,since the first conductor 22 and fourth conductor 27 are formed atremote positions from the second conductor 23 and third conductor 26,the magnetic fluxes generated in the first conductor 22 and fourthconductor 27 do not cancel each other, and the impedance value in thenormal mode can be enhanced.

The square third magnetic sheet 30 is formed between the first coil 21and second coil 25 (between the second conductor 23 and third conductor26). By the third magnetic sheet 30, the second conductor 23 and thirdconductor 26 are insulated from each other. The square fourth magneticsheet 31 is formed on the lower surface of the first coil 21 (lowersurface of the first conductor 22) and the upper surface of the secondcoil 25 (upper surface of the fourth conductor 27).

The magnetic sheets 24, 28, 30, 31 are composed of a mixture of ferritepowder oxide and resin, and a resin composite material mixing resin andferrite, glass ceramic, or other derivatives may be used. When using theresin, the baking process can be skipped as described below. Besides, bylaminating in the vertical direction, a square and flat magnetic member32 is formed. The magnetic member 32 may also have a certain thickness,not being limited to be flat. The magnetic member 32 is not alwaysrequired to be square. The thickness may be adjusted properly dependingon the required characteristics (impedance, withstand voltage, etc.),and the thickness may be adjusted by varying the thickness of themagnetic sheet itself, or by changing the number of magnetic sheets tobe formed.

The magnetic member 32 is impregnated with fluorine silane couplingagent, and the water-repellent fluorine silane coupling agent permeatesinto fine pores in the magnetic member 32, so that the humidityresistance of the noise filter can be enhanced.

Of the external electrodes 33 a, 33 b, 33 c, 33 d formed at both ends ofthe magnetic member 32, 33 a and 33 c are formed at one end of themagnetic member 32, and 33 b and 33 d are formed at other end of themagnetic member 32. The external electrodes 33 a, 33 b, 33 c, 33 d areplated with low melting metal such as nickel, tin or solder on thesurface of the conductors of silver or the like.

The both ends of the first coil 21, that is, the first leading-outportion 22 a and second leading-out portion 23 a are electricallyconnected to the external electrode 33 a and external electrode 33 b,respectively.

Similarly, in the second coil 25, the third leading-out portion 26 a iselectrically connected to the external electrode 33 c, and the fourthleading-out portion 27 a to the external electrode 33 d. That is, thefirst conductor 22 and third conductor 26 are drawn out to one end ofthe magnetic member 32, and the second conductor 23 and fourth conductor27 are drawn out to the other end of the magnetic member 32.

By forming the second conductor 23 and third conductor 26 in a spiralshape, the conductor length can be extended, and the overlap region ofthe second conductor 23 and third conductor 26 can be increased. As aresult, by passing the current in the second conductor 23 and thirdconductor 26 in a same direction, the impedance in the common mode canbe further heightened.

At least the second conductor 23 and third conductor 26 are formed byelectrocasting method, and a smaller conductor width and narrowerconductor pitch can be realized, and the length of the spiral secondconductor 23 and third spiral conductor 26 can be further extended. As aresult, the overlap region of the second conductor 23 and thirdconductor 26 is much increased, and by passing the current in the secondconductor and third conductor in the same direction, the magnetic fluxesgenerated in the second conductor and third conductor can furtherreinforce each other, and the impedance in the common mode become muchhigher.

On the other hand, when the conductors are formed by printing, theprecision of the mask is limited, and smaller conductor width andnarrower conductor pitch are not realized, and the impedance in thecommon mode can be increased only to a certain extent.

Further, when the second conductor 23 and third conductor 26 are spiraland the current flows from the external electrodes 33 a, 33 c drawn outin the same direction to the external electrodes 33 b, 33 d, in a planview from above the magnetic member 32, the current flows in the samedirection (clockwise or counterclockwise) in the second conductor 23 andthird conductor 26, and the impedance in the common mode is heightenedin such configuration. Accordingly, there is no problem if the firstconductor 22 and fourth conductor 27 are deviated in position in a planview from above the magnetic member 32, or different in the windingdirection with respect to the second conductor 23 and third conductor26. Not limited to a spiral shape formed on a plane, spiral lamination,arch or other shape may be possible. In the vortical or spiral shape,however, the generated magnetic flux is strong. For heightening theimpedance in the normal mode, the spiral shape is preferred. In the caseof a linear shape, the generated magnetic flux is weak and it is notsuited to the purpose of the invention.

FIG. 3( a) is a diagram showing the impedance characteristic when normalmode and common mode current flows in the noise filter in embodiment 1of the invention.

At this time, in each mode current, the frequency was varied, and theimpedance between the input and output terminals was measured (themeasuring circuit is shown in FIG. 3( b)). Samples were conductors 22,23, 26, 27 measuring 600 μm×600 μm in overall dimensions (vertical andlateral dimensions excluding the leading-out portions 22 a, 23 a, 26 a,27 a), with the number of turns of 4.

As clear from FIG. 3( a), the noise filter in embodiment 1 of theinvention can heighten the impedance in both normal mode and commonmode.

FIGS. 4( a) to (d) are top views of conductors 22, 23, 26, 27 of thenoise filter in embodiment 1 of the invention.

If the first conductor 22 is replaced by the second conductor 23, theexternal electrodes 33 a and 33 b are formed at one end of the magneticmember 32, and the external electrodes 33 c and 33 d at other end. Thispattern is called pattern B, and the pattern explained above is patternA. The first conductor 22 and second conductor 23 are nearly identicalin shape in a plan view as seen from above the magnetic member 32,except for the leading-out portions 22 a, 23 a, and therefore thecharacteristics are hardly changed (the sectional view at this time isshown in FIG. 4( e)).

The pattern A (embodiment 1 of the invention) is formed by laminatingthe first conductor 22, second conductor 23, third conductor 26, andfourth conductor 27 sequentially from the bottom, and pattern B isformed by laminating the second conductor 23, first conductor 22, thirdconductor 26, and fourth conductor 27 sequentially from the bottom.

Thus, if the vertical relation of the conductors 22, 23, 26, 27 ischanged, their shapes are almost identical except for the leading-outportions 22 a, 23 a, 26 a, 27 a, and therefore it is not needed toinspect the vertical relation of the conductors 22, 23, 26, 27, so thatthe productivity may be enhanced.

FIG. 5( a) is an equivalent circuit diagram of the noise filter (patternA) in embodiment 1 of the invention, and FIG. 5( b) is an equivalentcircuit diagram of the same noise filter (pattern B).

FIG. 6( a) is a diagram showing the impedance characteristics(attenuation characteristics) when a normal mode current is applied tothe noise filter of pattern A and noise filter of pattern B inembodiment 1 of the invention.

FIG. 6( b) is a diagram showing the direction of current applied to eachpattern, simulating pattern A and pattern B (pattern B1, pattern B2).Samples are same as in FIG. 3.

It is known from FIG. 6 that the attenuation characteristics varydepending on the direction of the applied current in the case of patternB.

This is because, in the noise filter (pattern A) in embodiment 1 of theinvention, the distance between the external electrodes 33 a, 33 cformed at one end of the magnetic member 32 and the vicinity of junction(leading-out portions 22 a, 26 a) of the first conductor 22 and thirdconductor 26, and the distance between the external electrodes 33 b, 33d formed at other end of the magnetic member 32 and the vicinity ofjunction (leading-out portions 23 a, 27 a) of the second conductor 23and fourth conductor 27 are equal to each other, and if the applieddirection of the normal mode current is different, the floating capacitygenerated in the magnetic member is invariable, and therefore if themounting direction on the substrate is different, the attenuationcharacteristics are not changed. It is hence not necessary to specifythe mounting direction on the substrate, and the steps of marking theproduct direction and others can be omitted.

In the case of pattern B, on the other hand, the distance between theexternal electrodes 33 a, 33 d formed at one end of the magnetic member32 and the vicinity of junction (leading-out portions 22 a, 27 a) of thefirst conductor 22 and fourth conductor 27, and the distance between theexternal electrodes 33 b, 33 c formed at other end of the magneticmember 32 and the vicinity of junction (leading-out portions 23 a, 26 a)of the second conductor 23 and third conductor 26 are different.Therefore, if the applied direction of the normal mode current isdifferent, the distance between the vicinities of junction (leading-outportion) close to the input and output parts is different, and thefloating capacity generated in the magnetic member varies, and theattenuation characteristics are changed, and it is necessary to mark theproduct direction.

However, in the case of pattern B (the first conductor 22 formedimmediately beneath the third conductor 26), the first conductor 22 andthird conductor 26 are nearly identical in shape except for theleading-out portions 22 a, 23 a, 26 a, 27 a, and the direction from thecenter of vortex to the outer side is counterclockwise in a plan view asseen from above the magnetic member 32, so that they are formed tooverlap in a plan view as seen from above the magnetic member 32. Atthis time, each overlap area can be increased to a maximum extent, andthe generated magnetic fluxes are mutually reinforced, and the impedanceof the common mode can be increased to a maximum extent.

In this embodiment 1, the external electrodes 33 a to 33 d are formed atboth ends of the magnetic member 32, but same effects are obtained ifformed at four corners in a top view of the magnetic member 32.

In the noise filter of embodiment 1 of the invention having suchconfiguration, its manufacturing method is explained below by referringto the accompanying drawings.

FIGS. 7( a) to (f) show the manufacturing method of the noise filteringembodiment 1 of the invention.

First, from a mixture of oxide of ferrite powder and resin, square firstmagnetic sheet 24, second magnetic sheet 28, third magnetic sheet 30,and fourth magnetic sheet 31 are fabricated.

At specified positions of the first magnetic sheet 24 and secondmagnetic sheet 28, a first via hole 24 a and a second via hole 29 areformed by laser, punching, or other drilling process. Preferably, whenthe via holes 24 a, 29 are filled with silver or other conductivematerial, the connection of the first conductor 22 and second conductor23, and that of the third conductor 26 and fourth conductor 27 areachieved more securely.

Next, as shown in FIG. 7( a), a mask is formed on a base plate 33 so asto expose patterns of conductors 22, 23, 26, 27, and the exposed portionis plated with silver and the mask is removed (electrocasting method),so that a plurality of spiral first conductor 22, second conductor 23,third conductor 26, and fourth conductor 27 made of silver or the likecan be manufactured.

The conductors 22, 23, 26, 27 have a first via electrode 22 b, a secondvia electrode 23 b, a third via electrode 26 b, and a fourth viaelectrode 27 b, respectively, positioned in the center of vortex at oneend, and have a first leading-out portion 22 a, a second leading-outportion 23 a, a third leading-out portion 26 a, and a fourth leading-outportion 27 a at the other end.

The conductors 22, 23, 26, 27 are almost identical in shape except forthe leading-out portions 22 a, 23 a, 26 a, 27 a. The leading-outportions 22 a, 23 a, and 26 a, 27 a are disposed at mutually confrontingpositions in the horizontal direction, so that the leading-out portion26 a may face the same direction as the leading-out portion 22 a.

Further, a plurality of first conductors 22 are formed on the top of thespecified number of fourth magnetic sheets 31, the first magnetic sheet24 having the first via hole 24 a is provided on the top of the firstconductors 22, and a plurality of second conductors 23 are provided onthe top of the first magnetic sheets 24, thereby forming the first coil21.

At this time, the first via electrode 22 b and second via electrode 23 bare connected through the first via hole 24 a, and the first conductor22 and second conductor 23 are electrically connected.

The third magnetic sheet 30 is formed on the top of the secondconductors 23.

A plurality of third conductors 26 are formed on the top of the thirdmagnetic sheets 30, the second magnetic sheet 28 having the second viahole 29 is provided on the top of the third conductors 26, and aplurality of fourth conductors 27 are provided on the top of the secondmagnetic sheets 28, thereby forming the second coil 25.

At this time, the third via electrode 26 b and fourth via electrode 27 bare connected through the second via hole 29, and the third conductor 26and fourth conductor 27 are electrically connected.

The laminating method of the conductors 22, 23, 26, 27 is not limited tothe above sequence, and, for example, the magnetic sheets may belaminated with each other after once forming on the magnetic sheets 24,28, 30, 31 formed beneath the conductors 22, 23, 26, 27.

A specified number of fourth magnetic sheets 31 are formed on the top ofthe fourth conductors 27, and laminated in the configuration as shown inFIG. 7( b).

As shown in FIG. 7( c), in one noise filter, the conductors 22, 23, 26,27 are cut off and incorporated by one piece each, and one laminatedbody 34 is obtained as shown in FIG. 7( d). At this time, the firstleading-out portion 22 a and third leading-out portion 26 a are exposedfrom both ends of the laminated body 34, and the second leading-outportion 23 a and fourth leading-out portion 27 a are exposed at otherends.

This laminated body 34 is baked, and a magnetic member 32 is formed.

The magnetic member 32 is chamfered as shown in FIG. 7( e).

Finally, as shown in FIG. 7( f), silver or other conductors are formedin the leading-out portions 22 a, 23 a, 26 a, 27 a exposed at both endsof the magnetic member 32, and their surfaces are plated with lowmelting metal such as nickel, tin or solder. As a result, the externalelectrode 33 a is formed in the first leading-out portion 22 a, externalelectrode 33 b is formed in the second leading-out portion 23 a,external electrode 33 c is formed in the third leading-out portion 26 a,and external electrode 33 d is formed in the fourth leading-out portion27 a, so that the noise filter in embodiment 1 of the invention ismanufactured.

After forming silver or other conductors, and before nickel plating, themagnetic member 32 is impregnated in fluorine silane coupling agent indecompressed atmosphere.

In the noise filter in embodiment 1 of the invention, by shortening thedistance between the second conductor 23 and third conductor 26 to havea large magnetic coupling, the impedance in common mode can beheightened, but if the distance between the second conductor 23 andthird conductor 26 is too close, the withstand voltage between thesecond conductor 23 and third conductor 26 is impaired, and the secondconductor 23 and third conductor 26 may be short-circuited.

Therefore the distance between the second conductor 23 and thirdconductor 26 (the thickness of the third magnetic sheet 30) should bespecified within a specific range.

FIG. 8 is a diagram showing the relation of the distance, couplingcoefficient, and withstand voltage between the second conductor 23 andthird conductor 26 of the noise filter in embodiment 1 of the invention.

The withstand voltage is tested by applying a voltage of 100 V betweenthe second conductor 23 and third conductor 26 for 1 minute, and therate of conforming samples (insulation resistance 108 ohms or more) isexpressed, and the axis of abscissas denotes the distance between thesecond conductor 23 and third conductor 26, and the axis of ordinatesrepresents the coupling coefficient and withstand voltage defectivepercentage. Samples are conductors 22, 23, 26, 27 measuring 600 μm×600μm in overall dimensions, with number of turns of 4.

As clear from FIG. 8, the distance between the second conductor 23 andthird conductor 26 should be 50 microns or longer and 200 microns orshorter. Thus, the withstand voltage between the second conductor 23 andthird conductor 26 is maintained, and the coupling coefficient betweenthe second conductor 23 and third conductor 26 is enhanced, so that theimpedance in common mode becomes higher.

The noise filter of this type generally measures 1.0 mm×1.0 mm×0.5 mmthick, and the vertical and lateral overall dimensions of the conductors22, 23, 26, 27 are usually 500 μm to 800 μm, and therefore in relationto the vertical and lateral overall dimensions of the conductors 22, 23,26, 27, the distance between the second conductor 23 and third conductor26 is ¼ to 1/16.

In these conditions, a magnetic coupling coefficient of 0.2 to 0.7 isobtained as clear from FIG. 8. Fluctuations of the coupling coefficientare due to change in the distance between the second conductor 23 andthird conductor 26 (when the conditions of the material of the magneticmember 32 and others are equal).

Further, the coupling coefficient also varies with the number of turnsof the conductors 22, 23, 26, 27. For example, when the number of turnsof the first conductor 22 and fourth conductor 27 is 1, and the numberof turns of the second conductor 23 and third conductor 26 is 6, thecoupling coefficient is 0.5 to 0.95. It is not realistic to have thedifference in the number of turns by 6 times or more, in embodiment 1 ofthe invention, the coupling coefficient of the noise filter is 0.2 to0.95. Hence, the impedance can be heightened in both common mode andnormal mode.

Thus, by varying the distance between the second conductor 23 and thirdconductor 26 and the number of turns of each conductor, the couplingcoefficient can be controlled to a desired value.

Or, as shown in FIG. 9, by setting in the relation of T1, T2>t, where T1is the distance between the first conductor 22 and second conductor 23,T2 is the distance between the third conductor 26 and fourth conductor27, and t is the distance between the second conductor 23 and thirdconductor 26, the floating capacity generated between the firstconductor and second conductor, between the third conductor and fourthconductor, and between the first conductor and fourth conductor can bedecreased. As a result, the impedance value elevates in the highfrequency region, and the distance between the first and fourthconductors can be extended, and the magnetic fluxes generated in thefirst and fourth conductors do not cancel each other, so that theimpedance in normal mode becomes higher.

FIG. 10 is a diagram of frequency characteristic showing improvement ofimpedance value in the high frequency region.

In FIG. 10, frequency characteristic C shows the case in which thedistance between the first conductor 22 and second conductor 23, andbetween the third conductor 26 and fourth conductor 27 is nearly same asthe distance between the second conductor 23 and third conductor 26,and, as shown in FIG. 9, frequency characteristic D shows the case inwhich the distance between the first conductor 22 and second conductor23, and between the third conductor 26 and fourth conductor 27 is longerthan the distance between the second conductor 23 and third conductor26, and the axis of ordinates represents the impedance, and the axis ofabscissas shows the frequency of applied current.

As clear from FIG. 10, the frequency showing the peak impedance ishigher in D than in C. That is, characteristic D has the noise removingproperty of higher frequency.

In the noise filter in embodiment 1 of the invention, other examples forenhancing the impedance in high frequency region are explained, but thefrequency changing rate varies with each condition.

Further, as shown in FIGS. 11( a) and (b), when a material 34 a lower inpermeability than the magnetic member 32 is disposed between the firstconductor 22 and second conductor 23, and between the third conductor 26and fourth conductor 27, the magnetic fluxes generated in the firstconductor 22 and fourth conductor 27 do not cancel each other, so thatthe impedance in normal mode becomes higher.

As the material 34 a lower in permeability, a non-magnetic material maybe disposed between the first magnetic sheet 24 and second magneticsheet 28, or part or whole of the first magnetic sheet 24 and secondmagnetic sheet 28 may be made of non-magnetic material, or thepermeability may be lowered by changing the composition of the magneticmaterial.

However, instead of forming a material 34 a of low permeability in allbetween the first conductor 22 and second conductor 23, and between thethird conductor 26 and fourth conductor 27 as shown in FIG. 11( a), itis more preferable to compose as shown in FIG. 11( b) in which at leasta material 34 a low in permeability is used together with the material(magnetic member 32) of high permeability disposed between the secondconductor 23 and third conductor 26, because the impedance in commonmode is higher. This is because the magnetic fluxes generated in thesecond conductor 23 and third conductor 26 are stronger by forming amaterial of high permeability between the two.

As shown in FIGS. 12( a) to (d), by setting the conductor length equalbetween external electrodes in the first and second coils 21, 25, sincethe total coil length including the leading-out portions 22 a, 23 a, 26a, 27 a is equal, the impedance values in the first and second coils 21,25 are equal.

As its means, the conductors 22, 23, 26, 27 are formed symmetrically tothe line 35 passing through the via electrodes 22 b, 23 b, 26 b, 27 b ofthe conductors. Point 36 is the intersection of the conductors 22, 23,26, 27 with the line 35. Moreover, the portions 37 of the leading-outportions 22 a, 23, 26 a, 27 a exposed to the end of the magnetic member32 are formed symmetrically to the line 35. Between the points 36 and37, the length of the leading-out portions 22 a, 23 a, 26 a, 27 a shouldbe equalized.

Further, as shown in FIG. 13, between the second conductor 23 and thirdconductor 26, when the density is set higher than in other parts, theporosity between the second conductor 23 and third conductor 26 can belowered, so that the withstand voltage between the second conductor 23and third conductor 26 can be assured.

At this time, a fifth magnetic sheet 38 of higher density than othermagnetic sheet (magnetic member 32) in the portion between the secondconductor 23 and third conductor 26 may be provided, and as the materialfor the fifth magnetic sheet 38, the content of sintering aid such asCuO or Bi2O3 may be increased, or the fifth magnetic sheet 38 of higherdensity than other magnetic sheet (magnetic member 32) may be used.

(Embodiment 2)

A noise filter in embodiment 2 of the invention is explained byreferring to the drawings.

The noise filter in embodiment 2 of the invention differs fromembodiment 1 of the invention only in that the first conductor 22 c andsecond conductor 23 c, and the third conductor 26 c and fourth conductor27 c are formed so as not to overlap in a plan view as seen from abovethe magnetic member 32, and other structure and manufacturing method aresame and are not explained herein.

FIGS. 14( a), (b), (d), and (e) are top views of the conductors 22 c, 23c, 26 c, 27 c of the noise filter in embodiment 2 of the invention, andFIGS. 14( c) and (f) are pattern see-through diagrams of the firstconductor 22 c and second conductor 23 c, and the third conductor 26 cand fourth conductor 27 c of the noise filter, respectively.

In FIG. 14, the first conductor 22 c and second conductor 23 c, and thethird conductor 26 c and fourth conductor 27 c are orthogonalrespectively, and they are formed so as not to overlap except for theorthogonal parts in a plan view as seen from above the magnetic member32. As a result, the floating capacity generated between the firstconductor 22 c and second conductor 23 c, and between the thirdconductor 26 c and fourth conductor 27 c can be decreased, and hence theimpedance value is elevated in the high frequency region.

Alternatively, the first conductor 22 c and fourth conductor 27 c may beformed so as not to overlap with the second conductor 23 c and thirdconductor 26 c in a plan view as seen from above the magnetic member 32.

The second conductor 23 c and third conductor 26 c are formed so that,when a current flows in the leading-out portions 23 a, 27 a (externalelectrodes 33 b, 33 d) from the leading-out portions 22 a, 26 a(external electrodes 33 a, 33 c) drawn out in the same direction, thecurrent may flow in the same direction (clockwise or counterclockwise)in a plan view as seen from above the magnetic member 32.

In the noise filter in embodiments 1 and 2 of the invention, two coils21 and 25 (impedance elements) are stacked up, but same effects areobtained by stacking up in plural layers.

In this case, the conductors adjacent in the vertical direction (commonimpedance elements) can heighten the impedance value in common mode, andthe conductors in the highest position and lowest position (normalimpedance elements) can heighten the impedance value in normal mode, andthe conductors between the common impedance element and normal impedanceelement have an intermediate value of the normal mode impedance andcommon mode impedance.

In this way, the impedance values in both normal mode and common mode,and the coupling coefficient expressing the degree of coupling of coilscan be easily adjusted and designed to desired values. Herein, when thecoupling coefficient is large, the impedance value in common modebecomes large.

The method of using the noise filter in embodiments 1 and 2 of theinvention in a pair of signal lines in the cellular phone or otherwireless communication appliance is explained.

For example, signal lines of communication wires in the headset of acellular phone are usually composed of a pair of cables (signal lines),and since the high frequency signal such as carrier of the cellularphone is superposed as radiation noise on the cables in normal mode andcommon mode, the effect of noise is likely to occur. For example, thisradiation noise may occur as noise in the audio signal.

The audio signal is disturbed by the high frequency noise in common modebecause the low frequency component in the signal is detected andsuperposed by the nonlinear element and electrostatic capacity in thecircuit.

For example, as shown in FIG. 15( a), when carrier 900 MHz (TDMAcarrier) in transmission and reception circuits of a cellular phone ofTDMA system is transmitted and received at 217 Hz (burst frequency), 217Hz is detected, and is superposed on the audio signal of normal mode,and audible noise may be heard. Therefore, if the current in common modeand normal mode to be induced can be suppressed, noise in audio outputcan be reduced.

As shown in FIG. 15( b), when the noise filters of embodiments 1, 2 ofthe invention were connected to a pair of signal lines (audio lines),the attenuation characteristics as shown in FIG. 15( c) were obtained.

As clear from FIG. 15( c), also by the carrier 900 MHz of the cellularphone, noise can be attenuated in both common mode and normal mode.Therefore, the signal of repetitive frequency 217 Hz detected togetherwith the carrier 900 MHz can be reduced, so that the audible noise maynot be heard.

In this way, when the noise filters in embodiments 1 and 2 of theinvention are connected in a pair of signal lines in the cellular phoneor wireless communication appliance, respectively to the first coil 21(first impedance element) and second coil 25 (second impedance element),in the pair of signal lines in which noises in both common mode andnormal mode are applied, impedances in both common mode and normal modecan be heightened (signals can be attenuated), so that the audible noisecan be reduced in audio lines such as a pair of signal lines.

(Embodiment 3)

A noise filter in embodiment 3 of the invention is explained below byreferring to the drawings.

FIG. 16 is a perspective exploded view of the noise filter in embodiment3 of the invention, FIG. 17( a) is a sectional view of line A—A of thenoise filter, and FIG. 17( b) is a perspective view of the noise filter.

In FIG. 16 and FIG. 17, a spiral first coil 121 is formed by laminatingand connecting first inner conductors 121 a to 121 f sequentially fromthe bottom. A spiral second coil 122 is formed by laminating andconnecting second inner conductors 122 a to 122 f sequentially from thebottom. That is, the first and second coils 121, 122 are composed of sixlayers each. However, the first and second coils 121, 122 are notrequired to be composed of six layers. The first inner conductors 121 ato 121 f, and second inner conductors 122 a to 122 f are made of silveror other conductive material.

The first inner conductors 121 a to 121 f, and second inner conductors122 a to 122 f are formed in U-shape except for the lowest and highestlayers thereof 121 a, 121 f, 122 a, 122 f. Not limited to U-shape,however, they may be formed in L- or other shape.

At this time, from the bottom sequentially, the first inner conductors121 a to 121 c, second inner conductor 122 a, first inner conductor 121d, second inner conductor 122 b, first inner conductor 121 e, secondinner conductor 122 c, first inner conductor 121 f, and second innerconductors 122 d to 122 f are formed, and the portion composed of thefirst inner conductors 121 to 121 c only is a first laminated body 123,the portion composed alternately of the first inner conductors andsecond inner conductors (the portion forming the second inner conductor122 a, first inner conductor 121 d, second inner conductor 122 b, firstinner conductor 121 e, second inner conductor 122 c, and first innerconductor 121 f) is a second laminated body 124, and the portioncomposed of the second inner conductors 122 d to 122 f only is a thirdlaminated body 125. That is, of the six-layer first and second coils121, 122, three layers are formed alternately.

Of the first inner conductors 121 a to 121 f, in the lowest layer andhighest layer 121 a, 121 f, first and second leading-out electrodes 126,127 are formed as the ends of the first coil 121. Similarly, in thesecond inner conductors 122 a, 122 f, third and fourth leading-outelectrodes 128, 129 are formed.

The leading-out electrodes 126, 127, 128, 129 may be also formed at fourcorners of the magnetic member 138 in a top view of the second innerconductor 122 f (magnetic member 138 described below).

A plurality of square first magnetic sheets 130 are formed beneath thefirst inner conductors 121 b, 121 c in the first laminated body 123, anda first via hole 131 is formed. Through this first via hole 131, thefirst inner conductors 121 a to 121 c are connected.

A plurality of square second magnetic sheets 132 are formed beneath thesecond inner conductors 122 d to 122 f in the third laminated body 125,and a second via hole 133 is formed. Through this second via hole 133,the second inner conductors 122 d to 122 f are connected.

A plurality of square third magnetic sheets 134 are formed beneath thesecond inner conductor 122 a, first inner conductor 121 d, second innerconductor 122 b, first inner conductor 121 e, second inner conductor 122c, and first inner conductor 121 f forming the second laminated body124, and a third via hole 135 and a fourth via hole 136 are formed (onlythe third via hole 135 is provided in the third magnetic sheet 134formed beneath the second inner conductor 122 a).

The first inner conductors 121 c and 121 d, 121 d and 121 e, and 121 eand 121 f are connected through the third via hole 135, respectively,and the second inner conductors 122 a and 122 b, 122 b and 122 c, and122 c and 122 d are connected through the four via hole 136,respectively.

That is, the fourth via hole 136 is formed in the third magnetic sheet134 having the third via hole 135 beneath the first inner conductor 121d. The first inner conductor 121 d is connected to the first innerconductor 121 c through this third via hole 135 and a third via hole 135provided in the third magnetic sheet 134 formed further beneath (abovethe first inner conductor 121 c), and the second inner conductor 122 bis connected to the second inner conductor 122 a through this fourth viahole 136 and a fourth via hole 136 provided in the third magnetic sheet134 formed further above (beneath the second inner conductor 122 b).

The third via hole 135 and second inner conductors 122 a to 122 c, andthe fourth via hole 136 and first inner conductors 121 d to 121 f areelectrically insulated from each other.

A plurality of square fourth magnetic sheets 137 are formed by aspecific number each beneath the first inner conductor 121 a and abovethe second inner conductor 122 f.

Magnetic sheets 130, 132, 134, 137 are composed of a mixture of oxide offerrite powder and resin, and a flat square magnetic member 138 isformed by laminating them in the vertical direction as described above.The magnetic member 138 may also have a certain thickness, not beinglimited to be flat. The magnetic member 138 is not always required to besquare. The thickness may be adjusted properly depending on the requiredcharacteristics (impedance, withstand voltage, etc.), and the thicknessmay be adjusted by varying the thickness of the magnetic sheet itself,or by changing the number of magnetic sheets to be formed.

The magnetic member 138 is impregnated with fluorine silane couplingagent, and the water-repellent fluorine silane coupling agent permeatesinto fine pores in the magnetic member 138, so that the humidityresistance of the noise filter can be enhanced.

Of the external electrodes 139 a, 139 b, 139 c, 139 d formed at bothends of the magnetic member 138, 139 a and 139 c are formed at one endof the magnetic member 138, and 139 b and 139 d are formed at other endof the magnetic member 138. The external electrodes 139 a, 139 b, 139 c,139 d are plated with low melting metal such as nickel, tin or solder onthe surface of silver or other conductors.

The external electrodes 139 a, 139 b, 139 c, 139 d may be also formed atfour corners of the magnetic member 138 in a top view of the magneticmember 138.

Both ends of the first coil 121, that is, the first leading-out portion126 and second leading-out portion 127 are electrically connected to theexternal electrode 139 a and external electrode 139 b, respectively.

Similarly, in the second coil 122, the third leading-out portion 128 iselectrically connected to the external electrode 139 c, and the fourthleading-out portion 129 to the external electrode 139 d.

As described herein, the noise filter in embodiment 3 of the inventionhas a three-layer structure consisting of the first laminated body 123composed of the first inner conductors 121 a to 121 c only, the secondlaminated body 124 alternately laminating the first inner conductors 121d, 121 e, 121 f and second inner conductors 122 a, 122 b, 122 c, beingformed on the top of the first laminated body 123, and a third laminatedbody 125 composed of the second inner conductors 122 d to 122 f only,being formed on the top of the second laminated body 124. Accordingly,when the current flows in a same direction in the first coil 121 andsecond coil 122 (clockwise or counterclockwise in a top view of themagnetic member 138), since the first inner conductors 121 d, 121 e, 121f and second inner conductors 122 a, 122 b, 122 c of the secondlaminated body 124 are formed alternately, the distance is closerbetween the alternately formed first inner conductors 121 d, 121 e, 121f and second inner conductors 122 a, 122 b, 122 c, so that the magneticfluxes generated in the first inner conductors 121 d, 121 e, 121 f andsecond inner conductors 122 a, 122 b, 122 c in the second laminated body124 may reinforce each other. As a result, the impedance in common modeis higher, and if current flows in reverse directions in the first coil121 and second coil 122, since only the first inner conductors 121 a to121 c are formed in the first laminated body 123 and only the secondinner conductors 122 d to 122 f are formed in the third laminated body125, the magnetic fluxes generated in the first inner conductors 121 ato 121 c formed in the first laminated body 123 and in the second innerconductors 122 d to 122 f formed in the third laminated body 125 do notcancel each other, so that the impedance in normal mode may be enhanced.

Therefore, if a current flows in a same direction in the first coil 121and second coil 122 (first inner conductors 121 d, 121 e, 121 f andsecond inner conductors 122 a, 122 b, 122 c in the second laminated body124), the impedance in the first inner conductors 121 d, 121 e, 121 fand second inner conductors 122 a, 122 b, 122 c becomes high, and theseinner conductors decrease the noise of the common mode. On the otherhand, when flowing in opposite directions, the impedance becomes high inthe first inner conductors 121 a to 121 c formed in the first laminatedbody 123 and the second inner conductors 122 d to 122 f formed in thethird laminated body 125, and these inner conductors decrease the noisein normal mode.

That is, since the impedance can be heightened in both common mode andnormal mode, the impedance of the common mode and normal mode can beadjusted to specified values individually.

FIG. 18 is an equivalent circuit diagram of the noise filter inembodiment 3 of the invention.

Incidentally, when the number of first inner conductors formed in thefirst laminated body 123 and the number of second inner conductorsformed in third laminated body 125 are different, if a current flows inreverse directions in the first coil 121 and second coil 122, theintensity of magnetic fluxes generated in the first inner conductorsformed in the first laminated body 123 and the second inner conductorsformed in the third laminated body 125 is different, so that theimpedance in normal mode entered from the first inner conductors may beset different from the impedance in normal mode entered from the secondinner conductors.

It is also effective to adjust the magnetic coupling coefficient finely.

That is, in this noise filter, the first and second coils 121, 122 areindividually composed of six layers, and three layers thereof, that is,half layers are formed alternately, but by varying the rate of thealternately formed portions (the rate of the inner conductors formed inthe second laminated body 24 of the whole inner conductors), the rate ofinner conductors capable of mutually reinforcing the generated magneticfluxes is changed, so that the coupling coefficient changes.

When the coupling coefficient can be thus finely adjusted, the impedancein common mode and impedance in normal mode can be controlled tospecified values, and this effect is outstanding.

Further, by maximizing or minimizing the rate of portions formedalternately, the coupling coefficient can be adjusted to a specifiedvalue between 0.2 to 0.95, and the impedance in normal mode and commonmode can be adjusted.

In the noise filter in embodiment 3 of the invention, FIG. 19( a) is adiagram showing the relation of the number of turns (the number of turnsof the first inner conductors 121 d to 121 f and second inner conductors122 a to 122 c) and coupling coefficient of internal conductors in thesecond laminated body 124, and FIG. 19( b) is a diagram showing therelation of the number of turns (the number of turns of the first innerconductors 121 a to 121 c and second inner conductors 122 d to 122 f)and coupling coefficient of internal conductors in the first laminatedbody 123 and third laminated body 125. Herein, one turn is counted whenthe inner conductor makes one turn in a top view of the magnetic member138. That is, when the inner conductor makes a ¼ turn, four layers arelaminated to make one turn.

Samples are magnetic members measuring 1.0 mm×1.0 mm×2.5 mm thick, withthe portion surrounded by the spiral first coil 121 and second coil 122measuring 600 μm×600 μm in a top view of the magnetic member. In FIG.19( a), the number of turns of the inner conductors is 1 in the firstlaminated body 123 and third laminated body 125, and in FIG. 19( b), thenumber of turns of the inner conductors is 10 in the second laminatedbody 124.

As clear from FIGS. 19( a), (b), the coupling coefficient is larger asthe number of turns of the inner conductors in the second laminated body124 is larger, the number of turns of the inner conductors in the firstlaminated body and third laminated body is smaller, and the thickness ofthe magnetic sheets 130, 132, 134 is thinner.

The coupling coefficient is 0.2 to 0.95 when the number of turns of theinner conductors in the second laminated body 124 is 10 or less and thenumber of turns of the inner conductors in the first laminated body andthird laminated body is 5 or more in the case of the thickness of themagnetic sheets 130, 132, 134 of 50 microns, and when the number ofturns of the inner conductors in the second laminated body 124 is 5 to11 and the number of turns of the inner conductors in the firstlaminated body and third laminated body is 4 or less in the case of thethickness of the magnetic sheets 130, 132, 134 of 100 μm.

As far as possible, meanwhile, when the number of turns of the innerconductors in the first laminated body and third laminated body issmaller and the number of turns of the inner conductors in the secondlaminated body 124 is larger, the coupling coefficient will be 0.95. Or,as far as possible, when the number of turns of the inner conductors inthe first laminated body and third laminated body is larger and thenumber of turns of the inner conductors in the second laminated body 124is smaller, the coupling coefficient will be 02.

Further, if the specified impedance in normal mode is obtained, theshape of the first inner conductors 121 a to 121 c formed in the firstlaminated body 123, and the shape of the second inner conductors 122 dto 122 f formed in the third laminated body 125 may not be limited,including the spiral, meandering or other shape formed on one plane.There is no problem if winding direction is reverse.

Incidentally, by bringing the first inner conductors 121 d, 121 e, 121 fand second inner conductors 122 a, 122 b, 122 c in the second laminatedbody 124 as close-to one turn as possible, the length of each innerconductor may be extended to a maximum extent, and therefore themagnetic fluxes generated in the first inner conductors 121 d, 121 e,121 f, and the second inner conductors 122 a, 122 b, 122 c can reinforceeach other, and if a current flows in a same direction in the first coil121 and second coil 122 (the first inner conductors 121 d, 121 e, 121 f,and the second inner conductors 122 a, 122 b, 122 c in the secondlaminated body 124), the impedance in common mode can be furtherenhanced.

In the noise filter in embodiment 3 of the invention having suchconfiguration, the manufacturing method is explained below by referringto the accompanying drawings.

FIGS. 20( a) to (g) are perspective views showing the manufacturingmethod of noise filter in embodiment 3 of the invention.

First, from a mixture of oxide of ferrite powder and resin, square firstmagnetic sheet 130, second magnetic sheet 132, third magnetic sheet 134,and fourth magnetic sheet 137 are fabricated.

Next, as shown in FIG. 20( a), a second via hole 133 is provided at aspecified position of the second magnetic sheet 132 by laser, punchingor other drilling process.

Further, as shown in FIG. 20( b), the second inner conductor 122 fhaving the fourth leading-out electrode 129 is formed by printing on thesecond magnetic sheet 132. At the same time, the second via hole 133 isfilled with silver or other conductive material. At this time, the endof the second inner conductor 122 f is connected to the second via hole133.

Same as in FIGS. 20( a), (b), the second inner conductors 122 d, 122 eare formed on the top of the second magnetic sheet 132 having the secondvia hole 133, the first inner conductors 121 d, 121 e, 121 f and secondinner conductors 122 a, 122 b, 122 c are formed on the top of the thirdmagnetic sheet 134 having the third via hole 135 and fourth via hole136, and the first inner conductors 121 a, 121 b, 121 c are formed onthe top of the first magnetic sheet 130 having the first via hole 131.

The inner conductors may be formed not only by printing, but also byother method such as plating, vapor deposition or sputtering.

Consequently, laminating in the configuration as shown in FIG. 20( c),spiral first and second coils 121, 122 are provided, and the firstlaminated body 123 composed of the first inner conductors 121 a to 121 conly, the second laminated body 124 formed on the top of the firstlaminated body 123 composed of the first inner conductors 121 d, 121 e,121 f and second inner conductors 122 a, 122 b, 122 c alternately, andthe third laminated body 125 formed on the top of the second laminatedbody 124 composed of the second inner conductors 122 d to 122 f only areformed.

As shown in FIG. 20( d), by cutting so that the first coil 121 andsecond coil 122 may be incorporated by one each in one noise filter, onelaminated body 140 as shown in FIG. 20( e) is obtained. At this time,the first leading-out electrode 126 and third leading-out electrode 128are exposed from both ends of the laminated body 140, and the secondleading-out electrode 127 and fourth leading-out electrode 129 areexposed at other ends.

This laminated body 140 is baked, and a magnetic member 138 is formed.

The magnetic member 138 is chamfered as shown in FIG. 20( f).

Finally, as shown in FIG. 20( g), silver or other conductors are formedin the leading-out electrodes 126, 127, 128, 129 exposed at both ends ofthe magnetic member 138, and their surfaces are plated with low meltingmetal such as nickel, tin or solder, and the external electrode 139 a isformed in the first leading-out electrode 126, external electrode 139 bis formed in the second leading-out electrode 127, external electrode139 c is formed in the third leading-out electrode 128, and externalelectrode 139 d is formed in the fourth leading-out electrode 129, andthe noise filter in embodiment 3 of the invention is manufactured.

After forming silver or other conductors, and before nickel plating, themagnetic member 138 is impregnated in fluorine silane coupling agent indecompressed atmosphere.

Herein, by setting the interval of the adjacent first inner conductors121 a to 121 c and second inner conductors 122 d to 122 f in the firstlaminated body 123 and third laminated body 125 larger than the intervalof the adjacent first inner conductors 121 d to 121 f and second innerconductors 122 a to 122 c in the second laminated body 124, it iseffective to decrease the floating capacity generated in the adjacentfirst inner conductors 121 a to 121 c and second inner conductors 122 dto 122 f in the first laminated body 123 and third laminated body 125,and in the first inner conductors 121 a to 121 c in the first laminatedbody 123 and the second inner conductors 122 d to 122 f in the thirdlaminated body 125. Accordingly, the impedance is enhanced in the highfrequency region, and the distance between the first inner conductors121 a to 121 c in the first laminated body 123 and the second innerconductors 122 d to 122 f in the third laminated body 125 can beextended. Therefore, the magnetic fluxes generated in the first innerconductors 121 a to 121 c in the first laminated body 123 and the secondinner conductors 122 d to 122 f in the third laminated body 125 do notcancel each other, and the impedance in normal mode is enhanced.

Further, by forming a sheet of a lower permeability than that of themagnetic member 138 between the adjacent first inner conductors 121 a to121 c and second inner conductors 122 d to 122 f in the first laminatedbody 123 and third laminated body 125, the magnetic fluxes generated inthe first inner conductors 121 a to 121 c in the first laminated body123 and the second inner conductors 122 d to 122 f in the thirdlaminated body 125 can be weakened, so that the impedance in normal modecan be lowered. Therefore, when the impedance in common mode isconstant, by controlling the impedance in normal mode, the couplingcoefficient can be adjusted.

Also by equalizing the length among the external electrodes in the firstand second coils 121, 122 (between 139 a and 139 b, and 139 c and 139d), the total coil length including the leading-out portions is equal,so that the impedance values may be same in the first and second coils121, 122.

Moreover, by setting the density of the magnetic member in the firstcoil 121 (first inner conductors 121 d to 121 f) and second coil 122(second inner conductors 122 a to 122 c) in the second laminated body124 higher than that of the magnetic member in other parts (firstlaminated body 123, third laminated body 125), it is effective to lowerthe porosity between the first coil 121 and second coil 122 (between thefirst inner conductors 121 d to 121 f and second inner conductors 122 ato 122 c in the second laminated body 124), so that the withstandvoltage between the first inner conductors 121 d to 121 f and secondinner conductors 122 a to 122 c in the second laminated body 124 may bemaintained.

(Embodiment 4)

A noise filter in embodiment 4 of the invention is explained byreferring to the drawings.

FIG. 21 is a perspective view of the noise filter in embodiment 4 of theinvention. In FIG. 21, a spiral first coil 141 is formed by laminatingand connecting first inner conductors 141 a to 141 i sequentially fromthe bottom. Reference numeral 142 is a spiral second coil, which isformed by laminating and connecting second inner conductors 142 a to 142i sequentially from the bottom. That is, the first and second coils 141,142 are composed of nine layers. The first and second coils 141, 142 arenot required to have nine-layer structure. The first inner conductors141 a to 141 i and second inner conductors 142 a to 142 i are made ofsilver or other conductive material.

The first inner conductors 141 a to 141 i and second inner conductors142 a to 142 i are formed in U-shape except for the lowest and highestlayers thereof 141 a, 141 i, 142 a, 142 i. Not limited to U-shape,however, they may be formed in L- or other shape.

More specifically, the first inner conductors 141 a to 141 d, firstinner conductor 141 e and second inner conductor 142 a formed on a sameplane, first inner conductor 141 f and second inner conductor 142 bformed on a same plane, first inner conductor 141 g and second innerconductor 142 c formed on a same plane, first inner conductor 141 h andsecond inner conductor 142 d formed on a same plane, first innerconductor 141 i and second inner conductor 142 e formed on a same plane,and second inner conductors 142 f to 142 i are formed sequentially fromthe bottom, and a portion composed of first inner conductors 141 a to141 d only forms a first laminated body 143, a portion composed of firstinner conductor and second inner conductor on a same plane (each portionforming the first inner conductor 141 e and second inner conductor 142a, first inner conductor 141 f and second inner conductor 142 b, firstinner conductor 141 g and second inner conductor 142 c, first innerconductor 141 h and second inner conductor 142 d, and first innerconductor 141 i and second inner conductor 142 e) forms a secondlaminated body 144, and a portion composed of second inner conductors142 f to 142 i only forms a third laminated body 145. That is, of thenine layers of the first and second coils 141, 142, five layers areformed on a same plane.

In the lowest and highest layers 141 a, 141 i of the first innerconductors 141 a to 141 i, first and second leading-out electrodes 146,147 are formed as the ends of the first coil 141. Similarly, third andfourth leading-out electrodes 148, 149 are formed in the second innerconductors 142 a, 142 i.

The leading-out electrodes 146, 147, 148, 149 may be also formed at fourcorners of the magnetic member 158 in a top view of the second innerconductor 142 i (magnetic member 158 described below).

A plurality of square first magnetic sheets 150 are formed beneath thefirst inner conductors 141 b to 141 d in the first laminated body 143,and a first via hole 151 is formed. Through this first via hole 151, thefirst inner conductors 141 a to 141 d are connected.

A plurality of square second magnetic sheets 152 are formed beneath thesecond inner conductors 142 f to 142 i in the third laminated body 145,and a second via hole 153 is formed. Through this second via hole 153,the second inner conductors 142 e to 142 i are connected.

A plurality of square third magnetic sheets 154 are formed beneath thefirst inner conductor 141 e and second inner conductor 142 a, firstinner conductor 141 f and second inner conductor 142 b, first innerconductor 141 g and second inner conductor 142 c, first inner conductor141 h and second inner conductor 142 d, and first inner conductor 141 iand second inner conductor 142 e formed respectively on a same plane ofthe second laminated body 144, and a third via hole 155 and a fourth viahole 156 are formed (only the third via hole 155 is provided in themagnetic sheet 154 formed beneath the first inner conductor 141 e andsecond inner conductor 142 a formed on a same plane).

The first inner conductors 141 e and 141 f, 141 f and 141 g, 141 g and141 h, and 141 h and 141 i are connected through the third via hole 155,respectively. The second inner conductors 142 a and 142 b, 142 b and 142c, 142 c and 142 d, and 142 d and 142 e are connected through the fourvia hole 156, respectively.

That is, the fourth via hole 156 is formed in the third magnetic sheet154 having the third via hole 155 beneath the first inner conductor 141f. The first inner conductor 141 f is connected to the first innerconductor 141 e through this third via hole 155, and the second innerconductor 142 b formed on the same plane as the first inner conductor141 f is connected to the second inner conductor 142 a through thisfourth via hole 156.

The first inner conductor and second inner conductor formed on a sameplane are electrically insulated from each other.

A plurality of square fourth magnetic sheets 157 are formed by aspecific number each beneath the first inner conductor 141 a and abovethe second inner conductor 142 i.

Magnetic sheets 150, 152, 154, 157 are composed of a mixture of oxide offerrite powder and resin, and a flat square magnetic member 158 (notshown) is formed by laminating them in the vertical direction asdescribed above. The magnetic member 158 may also have a certainthickness, not being limited to be flat. Or the magnetic member 158 isnot always required to be square. The thickness may be adjusted properlydepending on the required characteristics (impedance, withstand voltage,etc.), and the thickness may be adjusted by varying the thickness of themagnetic sheet itself, or by changing the number of magnetic sheets tobe formed.

The magnetic member 158 is impregnated with fluorine silane couplingagent, and the water-repellent fluorine silane coupling agent permeatesinto fine pores in the magnetic member 158, so that the humidityresistance of the noise filter can be enhanced.

Of the external electrodes 159 a, 159 b, 159 c, 159 d (not shown) formedat both ends of the magnetic member 158, 159 a and 159 c are formed atone end of the magnetic member 158, and 159 b and 159 d are formed atother end of the magnetic member 158. The external electrodes 159 a, 159b, 159 c, 159 d are plated with low melting metal such as nickel, tin orsolder on the surface of silver or other conductors.

The external electrodes 159 a, 159 b, 159 c, 159 d may be also formed atfour corners of the magnetic member 158 in a top view of the magneticmember 158.

Both ends of the first coil 141, that is, the first leading-outelectrode 146 and second leading-out electrode 147 are electricallyconnected to the external electrode 159 a and external electrode 159 b,respectively.

Similarly, in the second coil 142, the third leading-out electrode 148is electrically connected to the external electrode 159 c, and thefourth leading-out electrode 149 to the external electrode 159 d.

At this time, of the first inner conductor 141 e and second innerconductor 142 a, first inner conductor 141 f and second inner conductor142 b, first inner conductor 141 g and second inner conductor 142 c,first inner conductor 141 h and second inner conductor 142 d, and firstinner conductor 141 i and second inner conductor 142 e respectivelyformed on a same plane, the first inner conductors 141 c, 141 d, 141 e,141 f, 141 g are formed inside of the second inner conductors 142 a, 142b, 142 c, 142 d, 142 e.

As described herein, the noise filter in embodiment 4 of the inventioncomprises three layers, consisting of the first laminated body 143composed of the first inner conductors 141 a to 141 d only, the secondlaminated body 144 formed on the first laminated body 143 composed ofthe first inner conductor 141 e and second inner conductor 142 a, firstinner conductor 141 f and second inner conductor 142 b, first innerconductor 141 g and second inner conductor 142 c, first inner conductor141 h and second inner conductor 142 d, and first inner conductor 141 iand second inner conductor 142 e respectively formed on a same plane,and the third laminated body 145 formed on the second laminated body 144composed of the second inner conductors 142 f to 142 i only.Accordingly, when the current flows in a same direction in the firstcoil 141 and second coil 142 (clockwise or counterclockwise in a topview of the magnetic member 158), since the magnetic fluxes generated inthe first inner conductors 141 a to 141 i and second inner conductors142 a to 142 e of the second laminated body 144 reinforce each other,and the impedance in common mode is higher. Further, if current flows inreverse directions in the first coil 141 and second coil 142, since onlythe first inner conductors 141 a to 141 d are formed in the firstlaminated body 143 and only the second inner conductors 142 f to 142 iare formed in the third laminated body 145, the magnetic fluxesgenerated in the first inner conductors 141 a to 141 d formed in thefirst laminated body 143 and the second inner conductors 142 f to 142 iformed in the third laminated body 145 do not cancel each other, so thatthe impedance in normal mode may be enhanced.

Therefore, if a current flows in a same direction in the first coil 141and second coil 142 (first inner conductors 141 e to 141 i and secondinner conductors 142 a to 142 e in the second laminated body 144), theimpedance in the first inner conductors 141 e to 141 i and second innerconductors 142 a to 142 e becomes high, and these inner conductorsdecrease the noise of the common mode. On the other hand, when flowingin opposite directions, the impedance becomes high in the first innerconductors 141 a to 141 d formed in the first laminated body 143 and thesecond inner conductors 142 f to 142 i formed in the third laminatedbody 145, and these inner conductors decrease the noise in normal mode.

The equivalent circuit diagram of the noise filter in embodiment 4 ofthe invention is also shown in FIG. 18.

Incidentally, when the number of inner conductors formed in the firstlaminated body 143 and the number of second inner conductors formed inthird laminated body 145 are different, if a current flows in reversedirections in the first coil 141 and second coil 142, the intensity ofmagnetic fluxes generated in the first inner conductors formed in thefirst laminated body 143 and the second inner conductors formed in thethird laminated body 145 is different, so that the impedance in normalmode entered from the first inner conductors may be set different fromthe impedance in normal mode entered from the second inner conductors.

As described above, in the second laminated body 144, since the firstinner conductors 141 e, 141 f, 141 g, 141 h, 141 i are formed inside ofthe second inner conductors 142 a, 142 b, 142 c, 142 d, 142 e, thelength between external electrodes (159 a and 159 b, 159 c and 159 d) inthe first and second coils 141, 142 is different. As a result, theimpedance values of the first and second coils 141, 142 differ, but suchinconvenience may be eliminated by increasing the number of first innerconductors formed in the first laminated body 143 more than the numberof second inner conductors formed in the third laminated body 145, andby equalizing the distance between external electrodes (159 a and 159 b,159 c and 159 d) in the first and second coils 141, 142.

It is also effective to adjust the magnetic coupling coefficient finely.

That is, in this noise filter, the first and second coils 141, 142 areindividually composed of nine layers, and five layers thereof, that is,about 56% are formed on the same plane, but by varying the rate of theportions formed on the same plane (the rate of the inner conductorsformed in the second laminated body 144 of the whole inner conductors),the rate of inner conductors capable of mutually reinforcing thegenerated magnetic fluxes is changed, so that the coupling coefficientchanges.

When the coupling coefficient can be thus finely adjusted, the impedancein common mode and impedance in normal mode can be controlled tospecified values, and this effect is outstanding.

Further, by maximizing or minimizing the rate of portions formed on thesame plane, the coupling coefficient can be adjusted to a specifiedvalue between 0.2 to 0.95, and the impedance in normal mode and commonmode can be adjusted.

Further, if the specified impedance in normal mode is obtained, theshape of the first inner conductors 141 a to 141 d formed in the firstlaminated body 143, and the shape of the second inner conductors 142 fto 142 i formed in the third laminated body 145 may not be limited,including the spiral, meandering or other shape formed on one plane.There is no problem if winding direction is reverse.

Incidentally, by bringing the first inner conductors 141 e to 141 i andsecond inner conductors 142 a to 142 e in the second laminated body 144as close to one turn as possible, the length of each inner conductor maybe extended to a maximum extent, and therefore the magnetic fluxesgenerated in the first inner conductors 141 e to 141 i, and the secondinner conductors 142 a to 142 e can reinforce each other, and if acurrent flows in a same direction in the first coil 141 and second coil142 (the first inner conductors 141 e to 141 i and the second innerconductors 142 a to 142 e in the second laminated body 144), theimpedance in common mode can be further enhanced.

The manufacturing method is same as in embodiment 3 of the invention,basically, except that the forming positions of the inner conductors aredifferent, and the explanation is omitted.

Herein, by setting the interval of the adjacent first inner conductors141 a to 141 d and second inner conductors 142 f to 142 i in the firstlaminated body 143 and third laminated body 145 larger than the intervalof the first inner conductors and second inner conductors formed on asame plane in the second laminated body 144 (between the first innerconductor 141 e and second inner conductor 142 a, 141 f and 142 b, 141 gand 142 c, 141 h and 142 d, and 141 i and 142 e), it is effective todecrease the floating capacity generated in the adjacent first innerconductors 141 a to 141 d and second inner conductors 142 f to 142 i inthe first laminated body 143 and third laminated body 145, and in thefirst inner conductors 141 a to 141 d in the first laminated body 143and the second inner conductors 142 f to 142 i in the third laminatedbody 145. Accordingly, the impedance is enhanced in the high frequencyregion, and the distance between the first inner conductors 141 a to 141d in the first laminated body 143 and the second inner conductors 142 fto 142 i in the third laminated body 145 can be extended, and therefore,the magnetic fluxes generated in the first inner conductors 141 a to 141d in the first laminated body 143 and the second inner conductors 142 fto 142 i in the third laminated body 145 do not cancel each other, andthe impedance in normal mode is enhanced.

Further, by forming a sheet of a lower permeability than that of themagnetic member 138 between the adjacent first inner conductors 141 a to141 d and second inner conductors 142 f to 142 i in the first laminatedbody 143 and third laminated body 145, the magnetic fluxes generated inthe first inner conductors 141 a to 141 d in the first laminated body143 and the second inner conductors 142 f to 142 i in the thirdlaminated body 145 can be weakened, so that the impedance in normal modecan be lowered. Therefore, when the impedance in common mode isconstant, by controlling the impedance in normal mode, the couplingcoefficient can be adjusted.

Also by equalizing the length among the external electrodes in the firstand second coils 141, 142 (between 159 a and 159 b, and 159 c and 159d), the total coil length including the leading-out portions is equal,so that the impedance values may be same in the first and second coils141, 142.

Moreover, by setting the density of the magnetic member in the adjacentfirst coil 141 and second coil 142 in the second laminated body 144 (thefirst inner conductor 141 e and second inner conductor 142 a, 141 f and142 b, 141 g and 142 c, 141 h and 142 d, and 141 i and 142 e) higherthan that of the magnetic member in other parts (first laminated body143, third laminated body 145), it is effective to lower the porositybetween the first coil 141 and second coil 142 in the laminated body144, so that the withstand-voltage between the first coil 141 and secondcoil 142 in the second laminated body 144 may be maintained.

In the foregoing embodiments 3 and 4 of the invention, by setting thedistance between the first laminated body 123, 143 and the secondlaminated body 124, 144 (between the first inner conductor 121 c andsecond inner conductor 122 a, between the first inner conductor 141 dand second inner conductor 142 a), and between the second laminated body124, 144 and the third laminated body 125, 145 (between the first innerconductor 121 f and second inner conductor 122 d, between the firstinner conductor 141 i and second inner conductor 142 f) longer than thedistance between the adjacent inner conductors in the first laminatedbody 123, 143, second laminated body 124, 144, and third laminated body125, 145, it is effective to decrease the floating capacity generated inthe first inner conductors 121 a to 121 c, 141 a to 141 d in the firstlaminated body 123, 143, and second inner conductors 122 d to 122 f, 142f to 142 i in the third laminated body 125, 145 Accordingly, theimpedance is enhanced in the high frequency region, and the distancebetween the first inner conductors 121 a to 121 c, 141 a to 141 d in thefirst laminated body 123, 143 and the second inner conductors 122 d to122 f, 142 f to 142 i in the third laminated body 125, 145 can beextended, and therefore, the magnetic fluxes generated in the firstinner conductors 121 a to 121 c, 141 a to 141 d in the first laminatedbody 123, 143 and the second inner conductors 122 d to 122 f, 142 f to142 i in the third laminated body 125, 145 do not cancel each other, andthe impedance in normal mode is enhanced.

Further, by forming magnetic sheets of a lower permeability than that ofthe other magnetic sheets between the first laminated body 123, 143 andsecond laminated body 124, 144, and between the second laminated body124, 144 and third laminated body 125, 145, the magnetic fluxesgenerated in the first inner conductors 121 a to 121 c, 141 a to 141 din the first laminated body 123, 143 and the second inner conductors 122d to 122 f, 142 f to 142 i in the third laminated body 125, 145 do notcancel each other, so that the impedance in normal mode may be enhanced.

(Embodiment 5)

FIG. 22 is a perspective exploded view of a noise filter in embodiment 5of the invention, FIG. 23( a) is a sectional view of line A—A in FIG.22, and FIG. 23( b) is a top see-through diagram of the noise filter.

A spiral first coil 161 is formed by laminating and connecting firstinner conductors 161 a to 161 d sequentially from the bottom. A spiralsecond coil 162 is formed by laminating and connecting second innerconductors 162 a to 162 d sequentially from the bottom. That is, thefirst and second coils 161, 162 are composed of four layers. The firstand second coils 161, 162 are not required to have four-layer structure.The first inner conductors 161 a to 161 d and second inner conductors162 a to 162 d are made of silver or other conductive material.

The first inner conductors 161 a to 161 d and second inner conductors162 a to 162 d are formed in U-shape except for the lowest and highestlayers thereof 161 a, 161 d, 162 a, 162 d. Not limited to U-shape, theymay be formed in L- or other shape.

The first inner conductor 161 a, second inner conductor 162 a, firstinner conductor 161 b, second inner conductor 162 b, first innerconductor 161 c, second inner conductor 162 c, and first inner conductor161 d, second inner conductor 162 d are sequentially laminated from thebottom, that is, the first inner conductors 161 a to 161 d and secondinner conductors 162 a to 162 d are formed alternately. Further, asshown in FIG. 23( b), in a top view of the second inner conductor 162 d(a top view of a magnetic member 171 mentioned below), the area enclosedby the first coil 161 and the area enclosed by the second coil 162 areformed to overlap only in part individually.

That is, supposing the central axis of the spiral first coil 162 to be Band the central axis of the spiral second coil 161 to be C, B and C aredeviated.

Herein, B and C are deviated to such an extent that the area enclosed bythe first coil 161 and the area enclosed by the second coil 162 mayoverlap completely, or may not overlap completely in a top view (a topview of the magnetic member 171 mentioned below) of the second innerconductor 162 d of the first and second coils 161, 162.

In the lowest layer and highest layer 161 a, 161 d of the first innerconductors 161 a to 161 d, first and second leading-out electrodes 163,164 are formed as the ends of the first coil 161. Similarly, third andfourth leading-out electrodes 165, 166 are formed in the second innerconductors 162 a, 162 d.

The leading-out electrodes 163, 164, 165, 166 may be also formed at fourcorners of the magnetic member 171 in a top view of the second innerconductor 162 d (magnetic member 171 described below).

A plurality of square first magnetic sheets 167 are formed beneath thefirst inner conductors 161 b to 161 d, and second inner conductors 162 ato 162 d, and a first via hole 168 and a second via hole 169 are formed(only the first via hole 168 is formed in the first magnetic sheet 167formed beneath the second inner conductor 162 a, and only the second viahole 169 is formed in the first magnetic sheet 167 formed beneath thesecond inner conductor 162 d).

Through the first via hole 168, the first inner conductors 161 a and 161b, 161 b and 161 c, and 161 c and 161 d are connected. Through thesecond via hole 169, similarly, the second inner conductors 162 a and162 b, 162 b and 162 c, and 162 c and 162 d are connected.

That is, the second via hole 169 is formed in the first magnetic sheet167 having the first via hole 168 beneath the first inner conductor 161b. The first inner conductor 161 b is connected to the first via hole168 and the first inner conductor 161 a through the first via hole 168disposed in the first magnetic sheet 167 formed beneath it (above thefirst inner conductor 161 a), and the second inner conductor 162 b isconnected to the second via hole 169 and the second inner conductor 162a through the second via hole 169 disposed in the first magnetic sheet167 formed above it (beneath the inner conductor 162 b).

The first via hole 168 and second inner conductors 162 a to 162 d,andthe second via hole 169 and first inner conductors 161 a to 161 d areelectrically insulated from each other.

A plurality of square second magnetic sheets 170 are formed by aspecified number of sheets beneath the first inner conductor 161 a andabove the second inner conductor 162 d.

Magnetic sheets 167, 170 are composed of a mixture of oxide of ferritepowder and resin, and a flat square magnetic member 171 is formed bylaminating them in the vertical direction as described above. Themagnetic member 171 may also have a certain thickness, not being limitedto be flat. Or the magnetic member 171 is not always required to besquare. The thickness may be adjusted properly depending on the requiredcharacteristics (impedance, withstand voltage, etc.), and the thicknessmay be adjusted by varying the thickness of the magnetic sheet itself,or by changing the number of magnetic sheets to be formed.

The magnetic member 171 is impregnated with fluorine silane couplingagent, and the water-repellent fluorine silane coupling agent permeatesinto fine pores in the magnetic member 171, so that the humidityresistance of the noise filter can be enhanced.

Of the external electrodes 172 a, 172 b, 172 c, 172 d (not shown) formedat both ends of the magnetic member 171, 172 a and 172 c are formed atone end of the magnetic member 171, and 172 b and 172 d are formed atother end of the magnetic member 171. The external electrodes 172 a, 172b, 172 c, 172 d are plated with low melting metal such as nickel, tin orsolder on the surface of silver or other conductors.

The external electrodes 172 a, 172 b, 172 c, 172 d may be also formed atfour corners of the magnetic member 171 in a top view of the magneticmember 171.

Both ends of the first coil 161, that is, the first leading-outelectrode 163 and second leading-out electrode 164 are electricallyconnected to the external electrode 172 a and external electrode 172 b,respectively.

Similarly, in the second coil 162, the third leading-out electrode 165is electrically connected to the external electrode 172 c, and thefourth leading-out electrode 166 to the external electrode 172 d.

As shown in FIG. 24, meanwhile, the central axis B of the spiral firstcoil 161 and the central axis C of the spiral second coil 162 may bedeviated as explained in embodiment 5 of the invention, and it may bedesigned to comprise, as in embodiment 3 of the invention, a firstlaminated body composed of the first inner conductors only, a secondlaminated body formed on the top of the first laminated body,alternately laminating the first inner conductors and second innerconductors, and a third laminated body formed on the top of the secondlaminated body, composed of the second inner conductors only.

Or, as shown in FIG. 25( a), in a top view of the magnetic member 171,the area enclosed by the first coil 161 and the area enclosed by thesecond coil 162 may cross orthogonally in the portion shown in FIG. 23(b), or as shown in FIG. 5( b), in a top view of the magnetic member 171,the overlapping portion of the area enclosed by the first coil 161 andthe area enclosed by the second coil 162 may be diagonal.

Further, as shown in FIGS. 26( a), (b), spiral first and second coils161′, 162′ may overlap in part in a top view of the magnetic member.

As described herein, in the noise filter in embodiment 5 of theinvention, the spiral first coil 161 composed of first inner conductors161 a to 161 d and spiral second coil 162 composed of second innerconductors 162 a to 162 d are formed to overlap only in part, in thearea enclosed by the first coil 161 and the area enclosed by the secondcoil 162, in a top view of the magnetic member 171. When a current flowsin a same direction in the first coil 161 and second coil 162 (clockwiseor counterclockwise in a top view of the magnetic member 171), since thefirst inner conductors 161 a to 161 d and second inner conductors 162 ato 162 d are formed alternately, the distance of the alternately formedmutually adjacent first inner conductors 161 a to 161 d and second innerconductors 162 a to 162 d is closer. As a result, in a top view of themagnetic member 171 in the first coil 161 and second coil 162, themagnetic fluxes generated in the overlapped portions of area enclosed bythe first coil 161 and the area enclosed by the second coil 162 canreinforced with each other, and the impedance in common mode isenhanced, and if a current flows in opposite directions in the firstcoil 161 and second coil 162, in a top view of the magnetic member 171in the first coil 161 and second coil 162, the magnetic fluxes generatedin the non-overlapped portions of area enclosed by the first coil 161and the area enclosed by the second coil 162 do not cancel each other,so that the impedance in normal mode may be enhanced.

Therefore, when a current flows in a same direction in the first coil161 (first inner conductors 161 a to 161 d) and second coil 162 (secondinner conductors 162 a to 162 d), the impedance becomes higher in theoverlapped portion in a top view of the magnetic member 171 in the firstcoil 161 and second coil 162, and this portion lowers the noise incommon mode. If flowing in opposite directions, to the contrary, theimpedance becomes high in the non-overlapped portion in a top view ofthe magnetic member 171 in the first coil 161 and second coil 162, andthis portion lowers the noise in normal mode.

FIG. 27 is an equivalent circuit diagram of the noise filter inembodiment 5 of the invention. In the first coil 161 and second coil 162for heightening the impedance in normal mode, when the area is equal inthe non-overlapped portion in a top view of the magnetic member 171 inthe enclosed portion of the first coil 161 and enclosed portion of thesecond coil 162, the impedance in normal mode is equal, so that there isno directivity.

If the area is not equal in the non-overlapped portion in a top view ofthe magnetic member 171 in the enclosed portion of the first coil 161and enclosed portion of the second coil 162, when a current flows inopposite directions in the first coil 161 and second coil 162, theintensity of magnetic fluxes generated in the first coil 161 and secondcoil 162 is different. As a result, the impedance in normal mode enteredfrom the first coil 161 is different from the impedance in normal modeentered from the second coil 162.

Further, the magnetic coupling coefficient can be adjusted finely. Thatis, in this noise filter, by varying the overlapped portion area of thefirst and second coils 161, 162 in a top view of the magnetic member171, the rate of the inner conductors for reinforcing the generatedmagnetic fluxes mutually varies, so that the coupling coefficient ischanged.

When the coupling coefficient can be thus finely adjusted, the impedancein common mode and impedance in normal mode can be individually set todesired values, and this effect is outstanding.

Further, by maximizing or minimizing the area of overlapped portions ofthe first and second coils 161, 162 in a top view of the magnetic member171, the coupling coefficient can be adjusted to a specified valuebetween 0.2 to 0.95, and the impedance in normal mode and common modecan be adjusted.

Further, if the specified impedance in normal mode is obtained, theshape of the first inner conductors 161 a to 161 d and second innerconductors 162 a to 162 d may not be limited, including the spiral,meandering or other shape. There is no problem if winding direction isreverse.

Incidentally, by bringing the first inner conductors 161 a to 161 d andsecond inner conductors 162 a to 162 d as close to one turn as possible,the length of each inner conductor may be extended to a maximum extent,and therefore the magnetic fluxes generated in the first innerconductors 161 a to 161 d and second inner conductors 162 a to 162 d canreinforce each other, and if a current flows in a same direction in thefirst coil 161 and second coil 162, the impedance in common mode can befurther enhanced.

The manufacturing method is same as in embodiment 3 of the invention,basically, except that the forming positions of the inner conductors aredifferent, and the explanation is omitted.

Herein, by equalizing the length among the external electrodes in thefirst and second coils 161, 162 (between 172 a and 172 b, and 172 c and172 d), the total coil length including the leading-out portions isequal, so that the impedance values may be same in the first and secondcoils 161, 162.

Moreover, by setting the density of the magnetic member in the adjacentfirst inner conductors of the first coil 161 and second inner conductorsof the second coil 162 (the inner conductor 161 a and second innerconductor 162 a, 162 a and 161 b, 161 b and 162 b, etc.) higher thanthat of the magnetic member in other inner conductors, it is effectiveto lower the porosity between the first coil 161 and second coil 162(between the adjacent first inner conductor and second inner conductoreach), so that the withstand voltage may be maintained between the firstinner conductor 161 a and second inner conductor 162 a, 162 a and 161 b,161 b and 162 b (between the first coil 161 and second coil 162).

In the noise filters in the foregoing embodiments 3 to 5 of theinvention, the junctions of a pair of external electrodes formed at oneend of the magnetic member and the first coil and second coilelectrically connected to the external electrodes are formed above orbeneath, in a side view of the magnetic member, the junctions of a pairof external electrodes formed at other end of the magnetic member andthe first coil and second coil electrically connected to the externalelectrodes, and therefore if the direction is different when mounting onthe board, the attenuation characteristics are not changed.

In the noise filters in the foregoing embodiments 3 to 5 of theinvention, further as shown in FIG. 28( a) (which shows a sectional viewof the noise filter in embodiment 5 of the invention as an example), thejunctions 181 a, 181 b of a pair of external electrodes 181 formed atone end of the magnetic member 171 and the first coil 161 and secondcoil 162 electrically connected thereto are formed above, in a side viewof the magnetic member 171, the junctions 182 a, 182 b of a pair ofexternal electrodes 182 formed at other end of the magnetic member 171and the first coil 161 and second coil 162 electrically connectedthereto (pattern A). The equivalent circuit diagram of pattern A isshown in FIG. 18.

At this time, in a side view of the magnetic member 171, the junction181 a of the external electrode 181 formed at one end of the magneticmember 171 and the first coil 161, the junction 181 b of the externalelectrode 181 formed at one end of the magnetic member 171 and thesecond coil 162, the junction 182 a of the external electrode 182 formedat other end of the magnetic member 171 and the first coil 161, and thejunction 182 b of the external electrode 182 formed at other end of themagnetic member 171 and the second coil 162 are formed sequentially fromthe top. It is same if the first coil 161 and second coil 162 areexchanged.

By contrast, the junctions 181 a, 181 b of a pair of external electrodes181 formed at one end of the magnetic member 171 and the first coil 161and second coil 162 electrically connected thereto may be formed, asshown in FIG. 28( b), either above or beneath, in a side view of themagnetic member 171, the junctions 182 a, 182 b of a pair of externalelectrodes 182 formed at other end of the magnetic member 171 and thefirst coil 161 and second coil 162 electrically connected thereto, or,as shown in FIG. 28( c), may be formed between the junctions 182 a and182 b (pattern B). FIG. 28( c) shows the mounting direction is changed(inverted) from the configuration in FIG. 28( b).

FIG. 28( d) shows the relation (attenuation characteristics) offrequency and attenuation of noise filters of pattern A and pattern B inembodiments 3 to 5 of the invention. The same samples as in FIG. 19 wereused. In the diagram, A, B, C correspond to FIGS. 28( a), (b), (c).

As clear from FIG. 28( d), in embodiments 3 to 5 of the invention, thenoise filter of pattern A is free from fluctuation in the attenuationcharacteristics, but pattern B fluctuates (when the current direction ischanged). The equivalent circuit diagram of pattern B is shown in FIG.29.

This is because, in the noise filters of pattern A in embodiments 3 to 5of the invention, the distance between the junctions 181 a and 181 b ofa pair of external electrodes 181 formed at one end of the magneticmember 171 and the first coil 161 and second coil 162, and the distancebetween the junctions 182 a and 182 b of a pair of external electrodes182 formed at other end of the magnetic member 171 and the first coil161 and second coil 162 are equal to each other, and therefore if theapplied direction of the normal mode current is different (the currententering from 181 a and leaving from 182 a further enters from 182 b andleaves from 181 a, or the current entering from 182 a and leaving from181 a further enters from 181 b and leaves from 182 a), the floatingcapacity generated in the magnetic member 171 (the floating capacitybetween the vicinity of input and vicinity of output) is not changed. Asa result, if the direction of mounting on the board is different, theattenuation characteristics are invariable.

In embodiments 3 and 4, if the number of inner conductors for composingthe first and second coils is equal, the impedance values in normal modeare equal, so that directivity does not exist.

When the noise filter in embodiments 3 to 5 of the invention is appliedin a pair of signal lines in cellular phone or other wirelesscommunication appliance, the same effects as in embodiment 1 and 2 shownin FIGS. 15( a), (b), (c) are obtained.

(Embodiment 6)

A common mode noise filter in embodiment 6 of the invention is explainedby referring to the drawings.

FIG. 30 is a perspective exploded view of the common mode noise filterin embodiment 6 of the invention, FIG. 31( a) is a sectional view ofline A—A of the same, and FIG. 31( b) is a perspective view thereof.

In FIG. 30 and FIG. 31, a spiral first coil 231 is formed by laminatingand connecting first inner conductors 231 a to 231 e sequentially fromthe bottom. A spiral second coil 232 is formed by laminating andconnecting second inner conductors 232 a to 232 e sequentially from thebottom. That is, the first and second coils 231, 232 are composed offive layers. However, the first and second coils 231, 232 are notlimited to five-layer structure. The first inner conductors 231 a to 231e and second inner conductor 232 a to 232 e are made of silver or otherconductive material.

Herein, the first inner conductors 231 a to 231 e and second innerconductors 232 a to 232 e are formed alternately.

That is, the first inner conductor 231 a, second inner conductor 232 a,first inner conductor 231 b, second inner conductor 232 b, first innerconductor 231 c, second inner conductor 232 c, first inner conductor 231d, second inner conductor 232 d, first inner conductor 231 e, and secondinner conductor 232 e are sequentially formed from the bottom.

The spiral first coil 231 formed by laminating the first innerconductors 231 a to 231 e and the spiral second coil 232 formed bylaminating the second inner conductors 232 a to 232 e are formed tooverlap with each other in a top view of a magnetic member 246 describedbelow.

The first inner conductors 231 a to 231 e and second inner conductors232 a to 232 e are formed in a nearly U-shape.

By forming in a nearly U-shape, a coil of one turn is formed bylaminating the inner conductors by two layers only, and the number oflayers may be smaller. As a result, the size is reduced, and thedistance of adjacent inner conductors is closer in each inner conductorfor forming the coil, so that the magnetic fluxes generated in the firstand second coils 231, 232 can reinforce each other.

Beneath the lowest layer 231 a of the first inner conductors 231 a to231 e, a first leading-out electrode 233 for connecting with the end ofthe first coil 231 is formed, and above the highest layer 231 e, asecond leading-out electrode 234 for connecting with the other end ofthe first coil 231 is formed. Similarly, in the second inner conductors232 a, 232 e, third and fourth leading-out electrodes 235, 236 areformed.

The leading-out electrodes 233, 234, 235, 236 may be also formed at fourcorners of the magnetic member 246 in a top view of the magnetic member246.

A plurality of square first magnetic sheets 237 are formed beneath thefirst inner conductors 231 b to 231 e, and are provided with a first viahole 238 and a second via hole 239. The first via hole 238 is connectedto each end of the first inner conductors 231 a to 231 e, and iselectrically insulated from the second via hole 239.

The second via hole 239 is formed to overlap with the first and secondcoils 231, 231 in a top view of the magnetic member 246.

A plurality of square second magnetic sheets 240 are formed beneath thesecond inner conductors 232 a to 232 e, and are provided with a thirdvia hole 241 and a fourth via hole 242. The fourth via hole 242 isconnected to each end of the second inner conductors 232 a to 232 e, andis electrically insulated from the third via hole 241.

The third via hole 241 is formed to overlap with the first and secondcoils 231, 232 in a top view of the magnetic member 246.

At this time, the first inner conductors 231 a to 231 e are connectedthrough the first via hole 238 and third via hole 241, and the spiralfirst coil 231 is obtained. Similarly, the second inner conductors 232 ato 232 e are connected through the second via hole 239 and fourth viahole 242, and the spiral second coil 232 is obtained.

That is, the second via hole 239 is formed in the first magnetic sheet237 having the first via hole 238 beneath the first inner conductor 231b. The first inner conductor 231 b is connected to the first innerconductor 231 a through the first via hole 238 and third via hole 241provided in the second magnetic sheet 240 further beneath it (above thefirst inner conductor 231 a), and the second inner conductor 232 b isconnected to the second inner conductor 232 a through the second viahole 239 and fourth via hole 242 provided in the second magnetic sheet240 further above it (beneath the second inner conductor 232 b).

The first inner conductors 231 a to 231 e and at least one of the secondinner conductors 232 a to 232 e adjacent to the first inner conductors231 a to 231 e are formed to nearly overlap in a top view of themagnetic member 246.

That is, each pair of first inner conductor 231 a and second innerconductor 232 a, first inner conductor 231 b and second inner conductor232 b, first inner conductor 231 c and second inner conductor 232 c,first inner conductor 231 d and second inner conductor 232 d, and firstinner conductor 231 e and second inner conductor 232 e are provided tooverlap in a top view of the magnetic member 246 (except for the formedportions of the via holes 238, 239, 241, 242).

A plurality of square third magnetic sheets 243 are formed beneath thefirst inner conductor 231 a and above the second inner conductors 232 e.Beneath the third magnetic sheet 243 formed beneath the first innerconductor 231 a, first and third leading-out electrodes 233, 235 areprovided, and above the third magnetic sheet 243 formed above the secondinner conductor 231 e, second and fourth leading-out electrodes 234, 236are provided.

A fifth via hole 244 is provided in the third magnetic sheet 243 formedon the top of the second inner conductor 232 e, and the second innerconductor 232 e and fourth leading-out electrode 236, and the firstinner conductor 231 e and (through the third via hole 241) secondleading-out electrode 234 are connected with each other respectivelythrough the fifth via hole 244.

Further, first and second via holes 238, 239 are provided in the thirdmagnetic sheet 243 formed beneath the first inner conductor 231 a, andthe first inner conductor 231 a and first leading-out electrode 233, andthe second inner conductor 232 a and (through the second via hole 239)third leading-out electrode 235 are connected with each otherrespectively through the first and second via holes 238, 239.

A specified number of fourth magnetic sheets 245 are formed beneath thefirst and third leading-out electrodes 233, 235, and above the secondand fourth leading-out electrodes 234, 236.

Magnetic sheets 237, 240, 243, 245 are composed of a mixture of oxide offerrite powder and resin, and a flat square magnetic member 246 isformed by laminating them in the vertical direction as described above.The magnetic member 246 may also have a certain thickness, not beinglimited to be flat. Or the magnetic member 246 is not always required tobe square. The thickness may be adjusted properly depending on therequired characteristics (impedance, withstand voltage, etc.), and thethickness may be adjusted by varying the thickness of the magnetic sheetitself, or by changing the number of magnetic sheets to be formed.

The magnetic member 246 is impregnated with fluorine silane couplingagent, and the water-repellent fluorine silane coupling agent permeatesinto fine pores in the magnetic member 246, so that the humidityresistance of the noise filter can be enhanced.

Of the external electrodes 247 a, 247 b, 247 c, 247 d formed at bothends of the magnetic member 246, 247 a and 247 c are formed at one endof the magnetic member 246, and 247 b and 247 d are formed at other endof the magnetic member 246. The external electrodes 247 a, 247 b, 247 c,247 d are plated with low melting metal such as nickel, tin or solder onthe surface of the conductors of silver or the like.

The external electrodes 247 a, 247 b, 247 c, 247 d may be also formed atfour corners of the magnetic member 246 in a top view of the magneticmember 246.

The first leading-out electrode 233 and second leading-out electrode 234connected to both ends of the first coil 231 are electrically connectedto the external electrode 247 a and external electrode 247 b,respectively.

Similarly, in the second coil 232, the third leading-out electrode 235is electrically connected to the external electrode 247 c, and thefourth leading-out electrode 236 to the external electrode 247 d.

In the common mode noise filter in embodiment 6 of the invention havingsuch configuration, the manufacturing method is explained below byreferring to the drawings.

FIGS. 32( a) to (c), and FIGS. 33( a) to (d) are perspective viewsshowing the manufacturing method of the common mode noise filter inembodiment 6 of the invention.

First, from a mixture of oxide of ferrite powder and resin, square firstmagnetic sheet 237, second magnetic sheet 240, third magnetic sheet 243,and fourth magnetic sheet 245 are fabricated.

Next, as shown in FIG. 32( a), a fifth via hole 244 is opened in aspecified position of the third magnetic sheet 243 by laser, punching orother drilling process.

Similarly, first and second via holes 238, 239 are provided at specifiedpositions of the first magnetic sheet 237. Third and fourth via holes241, 242 are provided at specified positions of the second magneticsheet 240, and first and second via holes 238, 239 are provided atspecified positions of the third magnetic sheet 243.

As shown in FIG. 32( b), second leading-out electrode 234 and fourthleading-out electrode 236 are formed on the third magnetic sheet 243having the fifth via hole 244. At the same time, the fifth via hole 244is filled with silver or other conductive material.

The first inner conductor 231 a is printed on the third magnetic sheet243 having the first via hole 238 and second via hole 239. The first viahole 238 and first leading-out electrode 233 are connected to the secondvia hole 239 and third leading-out electrode 235. At the same time, thefirst via hole 238 and second via hole 239 are filled with silver orother conductive material.

The second inner conductor 232 a is printed on the second magnetic sheet240. The end of the second inner conductor 232 a and the fourth via hole242 are connected. At the same time, the third via hole 241 and fourthvia hole 242 are filled with silver or other conductive material.

The first inner conductor 231 b is printed on the first magnetic sheet237. The end of the first inner conductor 231 b and the first via hole238 are connected. At the same time, the first via hole 238 and secondvia hole 239 are filled with silver or other conductive material.

The first and third leading-out electrodes 233, 235 are printed on thefourth magnetic sheet 245.

Same as above, the plurality of first magnetic sheets 237 and secondmagnetic sheets 240 are alternately laminated, and set in configurationas shown in FIG. 32( c). A specified number of fourth magnetic sheets245 are formed beneath the first and third leading-out electrodes 233,235, and above the second and fourth leading-out electrodes 234, 236.

At this time, by the first via hole 238 formed in the first magneticsheet 237 and the third via hole 241 formed in the second magnetic sheet240, the first inner conductors 231 a to 231 e are connected, and thefirst coil 231 is obtained. By the second via hole 239 formed in thefirst magnetic sheet 237 and the fourth via hole 242 formed in thesecond magnetic sheet 240, the second inner conductors 232 a to 232 eare connected, and the second coil 232 is obtained.

Through the fifth via hole 244 formed in the third magnetic sheet 243,the second inner conductor 232 e and fourth leading-out electrode 236,and the first inner conductor 231 e and (through the third via hole 241)second leading-out electrode 234 are connected respectively.

Further, through the first via hole 238 formed in the third magneticsheet 243, the first inner conductor 231 a and first leading-outelectrode 233 are connected with each other, and the through the fourthvia hole 242 formed beneath the second magnetic sheet 240, the secondinner conductor 232 a and (through the second via hole 239) thirdleading-out electrode 235 are connected with each other.

The inner conductors and leading-out electrodes may be formed not onlyby printing, but also by plating, vapor deposition, sputtering or othermethod.

Next, as shown in FIG. 33( a), by cutting off so that the first coil 231and second coil 232 may be incorporated by one piece each in one commonmode noise filter, one laminated body 248 is obtained as shown in FIG.33( b). At this time, the first leading-out electrode 233 and thirdleading-out electrode 235 are exposed from both ends of the laminatedbody 248, and the second leading-out electrode 234 and fourthleading-out electrode 236 are exposed at other ends.

This laminated body 248 is baked, and a magnetic member 246 is formed.

The magnetic member 246 is chamfered as shown in FIG. 33( c).

Finally, as shown in FIG. 33( d), silver or other conductors are formedin the leading-out electrodes 233, 234, 235, 236 exposed at both ends ofthe magnetic member 246, and their surfaces are plated with low meltingmetal such as nickel, tin or solder, and the external electrode 247 a isformed in the first leading-out electrode 233, external electrode 247 bis formed in the second leading-out electrode 234, external electrode247 c is formed in the third leading-out electrode 235, and externalelectrode 247 d is formed in the fourth leading-out electrode 236, sothat the common mode noise filter in embodiment 6 of the invention ismanufactured.

After forming silver or other conductors, and before nickel plating, themagnetic member 246 is impregnated in fluorine silane coupling agent indecompressed atmosphere.

In the common mode noise filter in embodiment 6 of the invention, sincethe first coil 231 and second coil 232 overlap in a top view of themagnetic member 246, and the first inner conductors 231 a to 231 e andat least one of the second inner conductors 232 a to 232 e adjacent tothese first inner conductors 231 a to 231 e are designed to overlapnearly in a top view of the magnetic member 246, if a current flows in asame direction in the first coil 231 and second coil 232 (clockwise orcounterclockwise in a top view of the magnetic member), the magneticfluxes generated in the first inner conductors 231 a to 231 e and secondinner conductors 232 a to 232 e reinforce each other, and further themagnetic fluxes generated in the adjacent first inner conductors 231 ato 231 e and second inner conductors 232 a to 232 e reinforce eachother, in particular. As a result, the impedance in common mode can befurther enhanced.

Therefore, when a current flows in a same direction in the first coil231 and second coil 232, the impedance in first inner conductors 231 ato 231 e and second inner conductors 232 a to 232 e becomes higher, andthese inner conductors decrease the noise in common mode.

Further, since the second via hole 239 and third via hole 241 are formedto overlap with the first and second coils 231, 232 in a top view of themagnetic member 246, the second via hole 239 and (vertically) connectedsecond inner conductors 232 a to 232 e can overlap with the first coil231 composed of the first inner conductors 231 a to 231 e in a top viewof the magnetic member 246. Similarly, the third via hole 241 and(vertically) connected first inner conductors 231 a to 231 e can overlapwith the second coil 232 composed of the second inner conductors 232 ato 232 e in a top view of the magnetic member 246. Thus, the first andsecond coils 231, 232 always overlap in a top view of the magneticmember 246, so that the impedance in common mode may be effectivelyenhanced. On the other hand, if the second via hole 239 and third viahole 241 do not overlap with the first and second coils 231, 232 in atop view of the magnetic member 246, the second via hole 239 and(vertically) connected second inner conductors 232 a to 232 e, and thethird via hole 241 and (vertically) connected first inner conductors 231a to 231 e do not overlap with the first and second coils 231, 232 in atop view of the magnetic member 246, near the connection area of thesecond via hole 239 and third via hole 241 in the inner conductors 231 ato 231 e, 232 a to 232 e.

Of course, since the first via hole 238 and fourth via hole 242 areconnected to the ends of the inner conductors 231 a to 231 e, 232 a to232 e, they overlap with the first and second coils 231, 232 in a topview of the magnetic member 246.

By equalizing the length of the first and second coils 231, 232including the leading-out electrodes 233 to 236, the impedance values inthe first and second coils 231, 232 may be equalized.

A method of using the common mode noise filter in embodiment 6 of theinvention in a pair of signal lines in a cellular phone or otherwireless communication device as an example of electronic appliance isexplained below.

Signal lines of communication wires such as a headset of a cellularphone, for example, are usually composed of a pair of cables (signallines), and since the high frequency signal such as carrier of cellularphone is superposed on the cable as radiation noise in normal mode andcommon mode, the effect of noise is likely to appear. For example, theradiation noise superposed in common mode may appear as noise of audiosignal.

Audio and other signals are disturbed by high frequency noise of commonmode because the low frequency components in the signal are detected andsuperposed by the nonlinear element and electrostatic capacity in thecircuit.

For example, as shown in FIG. 34( a), when the carrier 900 MHz (TDMAcarrier) in the transmission and reception circuit of a cellular phoneof TDMA system is transmitted and received at 217 Hz (burst frequency),217 Hz is detected, and is superposed on the audio signal in normalmode, and audible noise is heard. Therefore, if the induced current incommon mode can be suppressed, noise of audio output or the like can belowered.

An example of use of the common mode noise filter in embodiment 6 of theinvention is shown in FIG. 34( b).

FIG. 34( c) is a diagram showing the attenuation characteristic(relation between frequency and attenuation) of the common mode noisefilter in embodiment 6 of the invention.

As clear from FIG. 34( c), even at the carrier 900 MHz of the cellularphone, the common mode noise is attenuated. Therefore, the signal ofrepetitive frequency 217 Hz detected together with the carrier 900 MHzcan be lowered, so that the audible noise may not be heard.

INDUSTRIAL APPLICABILITY

As described herein, according to the invention, a noise filter high inimpedance in common mode and normal mode, and a common mode noise filterhigh in impedance in common mode can be realized. When they are appliedin signal lines in cellular phone or other wireless communicationdevices, noise can be attenuated. For example, in audio lines as a pairof signal lines, the audible noise can be reduced.

1. A noise filter comprising a magnetic member formed by laminatingmagnetic sheets in a vertical direction, a first impedance elementformed in said magnetic member, a second impedance element formed abovesaid first impedance element, and external electrodes formed at bothends of said magnetic member and connected electrically to each end ofsaid first and second impedance elements, wherein said first impedanceelement includes a first normal impedance element and a first commonimpedance element connected electrically to said first normal impedanceelement above said first normal impedance element, said second impedanceelement includes a second common impedance element and a second normalimpedance element connected electrically to said second common impedanceelement above said second common impedance element, and said firstcommon impedance element and second common impedance element areopposite to each other, and are insulated from each other.
 2. A noisefilter comprising a magnetic member formed by laminating magnetic sheetsin a vertical direction, plural impedance elements formed in saidmagnetic member, and external electrodes formed at both ends of saidmagnetic member and connected electrically to each end of said pluralimpedance elements, wherein each impedance element is formed in verticaldirection, the impedance element formed in the lowest layer includes anormal impedance element and a common impedance element connectedelectrically to said normal impedance element above said normalimpedance element, the impedance element formed in the highest layerincludes a common impedance element and a normal impedance elementconnected electrically to said common impedance element above saidcommon impedance element, and other impedance elements have two commonimpedance elements mutually connected electrically and disposed invertical direction, and the common impedance elements are opposite toeach other and insulated from each other.
 3. The noise filter of claim1, wherein: said first normal impedance element is a spiral firstconductor; said first common impedance element is a spiral secondconductor; said second coming impedance element is a spiral thirdconductor; said second normal impedance element is a spiral fourthconductor; said second conductor is laminated above said firstconductor; and said fourth conductor is laminated above said thirdconductor.
 4. The noise filter of claim 2, further comprising: laminatedconductors; the normal impedance element and the common impedanceelement of the lowest layer are spiral conductors; the normal impedanceelement and the common impedance element of the highest layer are spiralconductors; and the two common impedance elements of the each of theother impedance elements are spiral conductors.
 5. The noise filter ofclaim 3, wherein a distance between the second conductor and the thirdconductor is longer than 50 μm and shorter than 200 μm.
 6. The noisefilter of claim 4, wherein a distance between the adjacent conductorsnot electrically connected is longer than 50 μm and shorter than 200 μm.7. The noise filter of claim 3, wherein a distance between the firstconductor and the second conductor and the distance between the thirdconductor and the fourth conductor are longer than the distance betweenthe second conductor and the third conductor.
 8. The noise filter ofclaim 3, wherein a material of low permeability is disposed between thefirst conductor and the second conductor, and between the thirdconductor and the fourth conductor.
 9. The noise filter of claim 1,wherein a length of the conductor between the external electrodes of thefirst impedance element is the same as a length of the conductor betweenthe external electrodes of the second impedance element.
 10. The noisefilter of claim 3, wherein a length of the conductor between theexternal electrodes of the first coil is the same as the length of theconductor between the external electrodes of the second coil.
 11. Thenoise filter of claim 1, wherein a density of the magnetic memberbetween the first common impedance element and the second commonimpedance element is higher than a density of a remainder of the noisefilter.
 12. The noise filter of claim 3, wherein a density of themagnetic member between the second conductor and the third conductor ishigher than a density in a remainder of the noise filter.
 13. The noisefilter of claim 1, wherein at least the first common impedance elementand the second common impedance element are formed by electrocasting.14. The noise filter of claim 3, wherein at least the second conductorand the third conductor are formed by electrocasting.
 15. The noisefilter of claim 1, wherein the first normal impedance element and thefirst common impedance element, and the second common impedance elementand the second normal impedance element are formed so as not to overlapeach other in a top view of the magnetic member.
 16. The noise filter ofclaim 3, wherein the first conductor and the second conductor, and thethird conductor and the fourth conductor are formed so as not to overlapeach other in a top view of the magnetic member.
 17. The noise filter ofclaim 1, wherein the first normal impedance element and the secondcommon impedance element are connected to the external electrode formedat one end of the magnetic member, and the first common impedanceelement and the second normal impedance element are connected to theexternal electrode formed at the other end of the magnetic member. 18.The noise filter of claim 3, wherein the first conductor and the thirdconductor are connected to the external electrode formed at one end ofthe magnetic member, and the second conductor and the fourth conductorare connected to the external electrode formed at the other end of themagnetic member.
 19. An electronic device, wherein the first impedanceelement and the second impedance element of the noise filter in claim 1are connected to a pair of signal lines in a wireless communicationdevice.
 20. The noise filter of claim 3, wherein a coupling coefficientbetween the second and third conductor is 0.2 to 0.95.
 21. An electronicdevice, wherein the first conductor, the second conductor, the thirdconductor and the fourth conductor of the noise filter of claim 3 areconnected to a pair of signal lines in a wireless communication device.22. The noise filter of claim 1, wherein the magnetic member isimpregnated with fluorine silane coupling agent.
 23. The noise filter ofclaim 4, wherein a coupling coefficient between the second and thirdconductor is 0.2 to 0.95.
 24. The noise filter of claim 2, wherein themagnetic member comprises a fluorine silane coupling agent.
 25. Thenoise filter of claim 3, wherein the magnetic member comprises afluorine silane coupling agent.